とする (to suru): Meaning, Grammar and Usage in Japanese

How to make assumptions with とする: non-past and ～た forms, the volitional form としよう, the choice of は, が, or を, and how としたら, とすれば, and とすると differ.

Category: Grammar Dissections

What does とする (to suru) mean in Japanese, and how do としたら, とすれば, and とすると differ?

In the use examined in this article, とする (to suru) means “to posit or adopt a proposition as a premise”.

としたら (to shitara)・とすれば (to sureba)・とすると (to suru to) are conjunctions that turn this operation into a condition, and all three can be rendered as “if we suppose that…”.

The differences are tendencies, not absolute rules:

• とすると more readily foregrounds the conclusion drawn from the hypothesis;
• とすれば foregrounds the premise adopted as a condition;
• としたら, more conversational and less constrained, lends itself more readily to imagined scenarios, questions, and the speaker’s personal evaluations.

Saying that something is true and deciding to treat it as true are not the same operation.

A sentence such as 彼が犯人だ directly presents a person as the culprit; 彼が犯人だとする, by contrast, takes the entire proposition “he is the culprit” and makes it the provisional basis of the reasoning: “suppose he is the culprit”, “let us assume that he is the culprit”, “let us proceed on the assumption that he is the culprit”.

Note that we are not saying “let us accept that he is the culprit”.

“Assuming or hypothesizing” and “conceding or accepting as true” are somewhat different concepts. In the first case, we formulate a hypothesis; in the second, we convey a stronger commitment, closer to believing or accepting that the person really is the culprit.

The first case is exactly where the operator とする comes into play, and this is precisely where its core meaning lies.

In the use we will examine, the construction is not primarily used to assert that what precedes it is true in the real world, but to establish that the content will be treated as valid within a particular framework.

The proposition may be plausible, doubtful, purely imaginary, or even already known: what matters is not its factual status, but the act by which the speaker adopts it as a premise, criterion, or starting point.

The usual translations—“suppose”, “assume”, “consider”, “posit that”—correctly describe the result of this operation, but they risk obscuring how it works internally.

とする is not an indivisible grammatical block. と presents content, while する performs the operation of adopting, fixing, or recognizing it in a particular way.

This same logic links apparently different uses such as formulating a hypothesis, establishing a rule, making a decision, assigning a function, or treating something as having a particular status or designation.

Likewise, とすると・とすれば・としたら, which are simply the “conjunctive forms” of とする (that is, versions of とする that connect two clauses), become much more transparent once this structure has been reconstructed.

They are not three arbitrary expressions that all mean, more or less, “if”: they result from applying と・ば・たら to the verb する.

First, content is posited as a premise through ～とする; then, this same operation is turned into a condition. The overall meaning is therefore not merely “if P”, but more precisely “if we take P as a premise” or “once P has been posited as the basis of the reasoning”.

The three forms share this fundamental mechanism, but they are not completely interchangeable. とすると・とすれば・としたら retain the different perspectives characteristic of と・ば・たら: they can affect how the hypothesis is presented, the relationship between premise and consequence, and the degree of the speaker’s subjective involvement.

The difference therefore does not lie in the general idea of “supposing”, which all three share, but in the way each construction invites the listener into the hypothetical scenario and leads them through its consequences.

Moreover, understanding the deeper meaning of とする is the key—or at least an excellent starting point—for fully grasping more complex forms such as として, としては, and としても.

These forms in fact originate in とする itself, and simply memorizing them without understanding what lies behind them can be limiting and can genuinely hinder comprehension of a conversation or text.

としても, for example, is a concessive construction whose meaning—and whose difference from other concessive forms, especially にしても and the simpler ても—can remain elusive unless its underlying logic is clear.

としては is often not very intuitive for learners, and when compared with its closest counterpart, にしては, it can be quite difficult to make sense of unless one can trace it back to its underlying core.

It is true that these uses are no longer equally transparent in contemporary Japanese and have undergone grammaticalization, with some of their meanings diverging from the original core; yet they are not expressions devoid of internal relationships either. Understanding in depth where they come from means building a solid foundation that prepares the way for genuine comprehension and avoids the need to memorize them mechanically.

In this article, then, we will begin with the anatomy of とする, examining how a proposition is transformed into a premise and how とすると・とすれば・としたら arise through the different conditional forms of する.

Only after reconstructing this shared operation can we understand what truly distinguishes the three forms and why Japanese chooses one rather than another.

とする (to suru): meaning and use for expressing assumptions in Japanese

The fundamental feature of とする is not the unreality of the hypothesis, but the shift in role assigned to the content that precedes it.

A proposition normally describes a situation and presents it as true: by adding とする, that same proposition ceases to function as the main assertion and becomes the object of a mental or discursive operation. The speaker is no longer merely talking about something, but establishing how a particular description of it is to be treated within the reasoning.

ここでは、彼がその事実を知らなかったとする。

Let us suppose here that he was unaware of that fact.

The content 彼がその事実を知らなかった, “he was unaware of that fact”, is not asserted directly. It is delimited by と and, through する, adopted as a valid scenario for the purposes of the analysis.

The sentence therefore does not inform the listener that the man was in fact unaware of the fact, nor does it necessarily suggest that this possibility is likely: it asks the listener to use it provisionally as a shared basis for reasoning. The translation “let us suppose that…” is natural and perfectly acceptable, but a more precise formulation would be “let us treat as valid, within the present framework, the proposition that…”.

The structure thus contains two distinct levels. Within the proposition, 彼 is the subject of 知らなかった; however, he is not the person formulating the hypothesis. The agent of the operation expressed by する is normally the speaker or writer, who remains implicit. The construction can be recomposed as follows:

[彼がその事実を知らなかった] + と +（話し手が）する

In this use, と does not necessarily introduce words spoken by someone. Its more general function is to enclose and present informational content as a recognizable unit; する, in turn, no longer retains the concrete meaning of “do”, but functions as a formal verb through which the speaker recognizes, adopts, or establishes that content.

This is why とする is not equivalent to a simple expression of doubt: it does not measure how strongly the speaker believes a proposition to be true, but determines the role that proposition is to play in the discourse.

The content posited through とする may in fact be uncertain, plausible, contrary to reality, or refer to the present, future, or past. It may even already be known and deliberately taken up again as a premise from which to restart the reasoning. What is temporarily suspended is not necessarily the speaker’s belief in the proposition, but its direct assertion as a fact about the real world.

Instead, the proposition acquires local validity: it is not necessarily accepted as reality, but it is to be treated as true within the scenario that has just been constructed.

This mechanism explains why とする can take different translations without losing its semantic core:

仮に彼が犯人だとする。

Let us suppose, for the sake of argument, that he is the culprit.

会議は中止とする。

The meeting is to be cancelled.

この値をゼロとする。

This value is taken to be zero.

In the first case, a hypothetical premise is established; in the second, a decision is made; in the third, an operational definition is fixed. “Hypothesize”, “establish”, “decide”, “define”, and “regard as” therefore do not represent completely independent meanings. In every case, とする performs the same fundamental operation: it takes content, an identity, or a relation and treats it as valid within a particular framework.

What changes is the nature of what is being posited and the pragmatic purpose for which it is done.

This function also explains the predominantly formal and argumentative character of the construction. とする occurs particularly naturally in proofs, theoretical explanations, problems, definitions, regulations, and texts in which the conditions of the reasoning need to be established explicitly.

Its relatively formal character does not depend on register alone: it reflects a perspective in which the hypothesis is presented as a controlled, shareable operation, kept separate from the speaker’s personal impressions.

The general meaning of とする can therefore be summarized not simply as “to suppose”, but as to posit content and grant it operational validity. The construction does not primarily say what is true: it establishes what is to be treated as true, decided, defined, or recognized within the discursive framework the speaker is building.

とすると・とすれば・としたら: meaning, formation, and differences

As noted above, とすると (to suru to)、とすれば (to sureba) and としたら (to shitara) are the “conjunctive forms” of とする. More precisely, they are its three conditional forms used conjunctively: the act of positing a premise no longer closes the sentence, but opens a subordinate clause and connects it to the judgment, question, or consequence that follows.

If we let P = the content adopted as a premise and Q = the judgment, question, or consequence that follows, their internal structure can be reconstructed as follows:

[P とする] + と → P とすると

[P とする] + ば → P とすれば

[P とする] + たら → P としたら

In the first form, there are two instances of と with different functions. The first is the と that delimits the content adopted as a premise; the second is the conditional と added to the verb する. P とすると therefore literally means “if the operation of assuming P is performed”.

In とすれば, by contrast, する takes the ば conditional form, すれば.

In としたら, it takes the たら form, したら. The た in したら does not necessarily place the hypothesis in the past: it belongs to the formation of the たら conditional. The time reference of the hypothesized content is determined by the proposition that precedes と.

The three constructions therefore do not add a condition directly to the premise. First, they turn the first clause into a premise through とする, and only then do they make the very act of adopting that premise conditional. The logical structure is not simply “if P happens, then Q happens”, but “if, for the purposes of the reasoning, we treat P as valid, what can we say on that basis?”.

来年、日本に留学するとしたら、今から何を準備すべきだろう。

If we assume that we’ll be studying in Japan next year, what should we start preparing now?

The preparation referred to in the second part must take place before the possible stay in Japan. This shows that the premise and the judgment/question that follows are not necessarily ordered according to the temporal sequence “first P, then Q”. The relevant condition is the assumption made in the present: by treating the future stay in Japan as a valid premise in the present, we can evaluate what needs to be done in advance.

The same mechanism allows a past content to be adopted as a premise and a conclusion valid in the present to be drawn from it:

彼がその事実を知らなかったとすれば、あの反応にも説明がつく。

If we assume that he did not know that fact, that reaction can also be explained.

The content preceding these forms normally appears in plain form. With nouns and な-adjectives, the affirmative present retains the copula だ or, in a more formal register, である: 学生だとすると, “if we assume that he is a student”; 静かだとすれば, “if we suppose that it is quiet”.

Negative and past contents are also possible, such as 来ないとしたら, “if we suppose that he will not come”, 学生だったとすれば, “if we assume that he was a student”, or 知らなかったとすると, “if we suppose that he did not know”. The proposition may also appear in the explanatory のだ form, as in 彼が来ないのだとしたら, “if it really is the case that he will not come”.

The premise does not necessarily have to appear in the same sentence. とすると・とすれば・としたら can anaphorically refer back to an entire preceding statement and function as genuine textual conjunctions, with meanings such as “if that is so”, “in that case”, or “starting from that”:

彼はすでに辞退したらしい。とすれば、次の候補は田中さんだ。

Apparently, he has already withdrawn. If so, the next candidate is Tanaka.

In this example, the premise is not a purely imaginary situation. The speaker has received some information and, without necessarily vouching for its truth personally, adopts it as the basis for an inference. The three forms can in fact introduce not only an uncertain or counterfactual hypothesis, but also an already established or reasonably reliable fact reformulated as a premise in an argument.

Their function is not to establish how probable P is, but to temporarily suspend direct assertion of P and declare: “let us reason from this premise”.

This mediation distinguishes the three constructions from simple conditionals:

雨が降ったら、試合を中止します。

If it rains, we will cancel the match.

雨が降るとしたら、夕方以降だろう。

If we assume it will rain, it will probably be sometime after late afternoon.

In the first example, たら directly links the possibility of rain to the decision to cancel the match. In the second, by contrast, the possibility of rain is first treated as a hypothesis to reason from; the sentence does not establish what will be done if it rains, but tries to determine when the rain might occur by provisionally accepting the possibility that it will.

The three forms share this same mechanism and, in many contexts, can replace one another without substantially changing the truth conditions of the sentence. The differences concern mainly how the speaker presents the transition from premise to conclusion.

They are not three rigid steps on a probability scale, and it is not correct to claim in absolute terms that one introduces real situations while another introduces unreal ones. Their nuances derive from the original properties of と・ば・たら, but are softened by the shared presence of とする.

とすると is particularly natural when presenting a deduction that follows from the premise. The conditional と normally tends to represent a stable or consequential relationship; when applied to とする, it transfers this force from the relationship between two events to the relationship between a hypothesis and what can logically be inferred from it.

Once the premise has been posited, what follows is presented as the conclusion, problem, or question that arises from it.

この仮説が正しいとすると、従来の説明は成立しない。

If we assume this hypothesis is correct, the conventional explanation does not hold up.

彼が犯人ではないとすると、誰がこの鍵を持っていたのだろう。

If we suppose that he is not the culprit, who could have had this key?

For this reason, とすると readily occurs in calculations, proofs, investigations, and lines of reasoning in which a premise is carried forward to its implications.

The impression of greater objectivity does not arise because P is necessarily more probable, but from the relatively impersonal way in which Q is presented as the result of the logical operation. Even a highly unreal hypothesis can be introduced with とすると:

仮に時間を逆に進められるとすると、因果関係をどう説明すべきだろう。

If, hypothetically, it were possible to make time run backwards, how should we explain the relationship between cause and effect?

とすれば retains more strongly the selective and conditional value of ば. It foregrounds the acceptance of P as the necessary basis of the reasoning: “if we take this particular proposition as our premise”, “if we reason within this hypothesis”.

Compared with とすると, it can make the speaker’s detachment from the assumed content more apparent, and it is particularly well suited to evaluations, argumentative conclusions, and contrasts between possibilities. It is frequent in written language and formal discourse, although it is not limited to those registers.

その証言が正しいとすれば、事件は午前零時より前に起きたことになる。

If we accept that testimony as correct, it follows that the incident occurred before midnight.

A characteristic pattern is あるとすれば、それは…, through which the speaker examines a set of possibilities and identifies the one that might satisfy the condition:

この計画に欠点があるとすれば、費用が高すぎることだ。

If this plan has a weakness, it is that the cost is too high.

The sentence does not directly assert that the plan has a flaw. The speaker provisionally entertains that possibility and, within it, identifies the cost as the only relevant candidate. This selective function makes とすれば particularly suitable for formulations such as “if there is a cause, it must be this one”, “if anyone can do it, it is him”, or “if there is a difference, this is what it consists in”.

としたら, by contrast, more readily constructs a concrete scenario and invites the speaker or listener to imagine it from within. It inherits from たら its naturalness with specific and circumscribed conditions and, of the three forms, is the one most common in conversation and most compatible with questions, wishes, preferences, and personal evaluations.

もし一つだけ願いがかなうとしたら、何を願う？

If you could have just one wish granted, what would you wish for?

一つだけ選べるとしたら、私はこの案を選びたい。

If I could choose only one, I would choose this proposal.

Its ability to prompt the imagination of a situation also makes it especially natural with counterfactual hypotheses:

あのとき別の道を選んでいたとしたら、人生はどう変わっていただろう。

If I had chosen a different path back then, how would my life have changed?

This does not mean that としたら necessarily expresses an unreal hypothesis. It can also refer to a concrete possibility or pick up information that has just been received. Unreality comes from the content and context, not from the form itself. Compared with とすると・とすれば, the construction nevertheless allows greater freedom in the main clause; immediate orders or decisions remain less natural, however.

If the speaker simply wants to give an instruction or state what they will do when an event occurs, ordinary たら or なら is often more appropriate. としたら retains the idea of a scenario being considered, rather than a practical condition already built into a course of action.

The different perspectives of the three constructions also emerge when the premise and conclusion remain identical:

この情報が正しいとすると、出発は明日の朝になる。

If we take this information as correct, it follows that departure will be tomorrow morning.

この情報が正しいとすれば、出発は明日の朝になる。

If we accept this information as correct, departure will be tomorrow morning.

この情報が正しいとしたら、出発は明日の朝になる。

If this information really were correct, departure would be tomorrow morning.

The three sentences can describe the same relationship. とすると more readily foregrounds the conclusion obtained from the premise; とすれば more clearly foregrounds the conditional acceptance of that premise; としたら presents the situation in a more dialogic and imaginative way.

These are pragmatic tendencies, not hard-and-fast boundaries: register, the type of main clause, and the purpose of the reasoning can make more than one form natural.

As a practical guideline:

• とすると is particularly suitable when the goal is to advance a deduction;
• とすれば is particularly suitable when the goal is to isolate and formally evaluate a premise;
• としたら is preferable when inviting someone to imagine a scenario or express a personal reaction.

In all three cases, however, the deeper meaning remains that of とする: P is not simply declared true, but is treated as conditionally valid within the immediate context, from which the discourse can proceed toward Q.

Formation and grammatical structure of とする

To construct a sentence with とする correctly, two levels must be distinguished: the form of the content adopted as a premise and the form taken by する. The first allows us to specify, for example, whether we are imagining a future event or a situation that has already occurred; the second allows us to present the assumption directly, propose it with としよう, or place it inside a conditional construction.

The basic construction: plain form + とする

When the hypothesis concerns the content of a proposition, the basic pattern is proposition in plain form + とする. By plain form we mean the form without the polite endings です and ます: not necessarily the dictionary form alone, but also negative forms, ～た forms, and forms describing an ongoing state or action.

With nouns and な-adjectives, an explicit propositional construction therefore retains the copula: 学生だとする, 一定だとする. In formal style, である can be used: 学生であるとする, 一定であるとする. い-adjectives, by contrast, connect directly to と: 高いとする. Their corresponding negative forms include, for example, 行かないとする, 高くないとする, 一定ではないとする, and 学生ではないとする.

Politeness can be expressed in the final part: 彼が来るとします keeps 来る inside the proposition and puts する into the polite form します. There is also a construction in which an element is assigned a particular value or qualification, as in 温度を一定とする; its structure will be clarified in the comparison between particles.

The verb before とする: non-past and ～た forms

Simply speaking of a “present tense” can be misleading. Japanese uses a non-past form, which may refer to the present or the future depending on the predicate and context. With an event such as passing an exam, the non-past can present a future event or outcome; with a stative predicate, it can describe a current situation.

彼が試験に合格するとする。

彼が試験に合格したとする。

In the first example, passing the exam is considered as a possibility.

In the second, it is presented as already having occurred within the scenario under consideration. This sentence can concern a past exam whose result is unknown to us: we provisionally assume that it was passed and reason from the consequences. The ～た form remains inside the hypothesis: it does not certify that the event actually happened.

The same form can also appear when the time reference is future:

明日の試験に合格したとする。

The exam is still in the future, but within the imagined situation it is represented as already passed. Mentally, we place ourselves in the scenario after the successful outcome.

For this reason, ～たとする does not always mean “to hypothesize something about the past”: it can also present a future event as already realized. Niwa’s grammar illustrates precisely this use with admission to university expected the following year, expressed using a ～た form before とします.

The choice between the non-past form and ～た therefore concerns the temporal placement and the perspective from which the event is viewed; by itself, it does not constitute a scale of probability. The time internal to the premise must also be distinguished from the final form: to hypothesize today about a past event, one can say 合格したとする, leaving する unchanged.

The volitional form としよう and how it differs from とする

The volitional form is obtained by changing する to しよう; the corresponding polite form is しましょう. The content preceding と retains its own form.

ここでは、温度は一定だとする。

ここでは、温度は一定だとしよう。

With とする, the premise is introduced directly into the reasoning.

With としよう, the invitation to adopt it becomes explicit: “let us take this hypothesis as our starting point”. In an explanation, this can involve the reader or listener in the procedure. The content of the assumption remains the same; what changes is how it is proposed.

It is not necessary for the verb inside the proposition to become volitional. 行くとする becomes 行くとしよう; 行ったとする becomes 行ったとしよう. Changing 行く to 行こう instead produces 行こうとする, a different construction that can express an attempt or the imminence of an action. The position of the inflection is therefore crucial.

Choosing the particle: は, が, and を

Consider three examples in the same context: a theoretical line of reasoning in which a constant temperature is assumed. The formulations can lead to the same premise, but they organize the information and grammatical relationships differently.

温度は一定だとする。

With は, the temperature is set up as the topic: it is the element we are talking about and with respect to which we formulate the assumption.

The sentence is suitable, for example, in an explanation where temperature, pressure, and volume are examined separately. If the context contrasts these quantities, は can also take on a contrastive value: as for the temperature, we regard it as constant, while for other quantities we adopt different assumptions. Contrast is a contextual possibility, not an obligatory meaning.

温度が一定だとする。

With が, 温度 is explicitly the subject of the predicate 一定だ.

The assumed content can be identified as a complete proposition: 温度が一定だ, “the temperature is constant”. が therefore identifies the subject of the hypothesized situation; it does not indicate who is formulating the hypothesis. This formulation allows the situation to be presented as a whole, without separately introducing “as for the temperature”. There is no need to attribute special emphasis to が in every occurrence.

温度を一定だとする。

With を, the temperature is presented as the object of the evaluation or assumption: it is the element to which we assign the property of being constant.

The presence of だ keeps the predication 一定だ explicit. This combination should not be ruled out merely because it contains を: Ōtsuka analyzes constructions with an object marked by を followed by a predication with だとする, showing the continuity between presenting a judgment and assigning a qualification to an object.

The temperature example illustrates how this distinction works in a hypothetical context.

To express the assumption in a more compact form, one can also write:

温度を一定とする。

Here the pattern element を + value or qualification とする is immediately visible. In the context of a theoretical model, を does not imply a physical intervention that makes the temperature constant: it identifies the datum being treated in that way within the reasoning. The construction with を is in fact also attested in assumptions, as when an income or a speed is fixed hypothetically.

Finally, は is not on the same level as が and を: it marks the topic and can replace the marking of an element that, without topicalization, would appear with one or the other particle.

For this reason, the mere presence of は does not always allow the underlying grammatical relationship to be reconstructed unambiguously. The particle, predicate, and context must be read together.

How とすると, とすれば, and としたら are formed

The three variants are formed by applying a conditional form to する, while the proposition preceding と retains its own structure.

In とすると, the two instances of と perform different functions: the first introduces the assumed content; the second conditionally links the assumption to what follows in the sentence. In とすれば and としたら, this conditional function is expressed by すれば and したら respectively. From the standpoint of formation, したら is obtained by adding ら to the form した.

The fact that としたら contains した does not force the content of the hypothesis into the past. The temporal reference remains determined by the proposition and the context:

明日、彼が来るとしたら、何時ごろだろう。

Here 来る refers to a future arrival, while したら makes the assumption conditional. With 来たとしたら, by contrast, the arrival is presented as already having occurred within the scenario under consideration: the two forms occupy different positions and do not replace one another.

The same linking rules apply to nouns, adjectives, and negative forms: 学生だとすれば, 一定だとすると, 高くないとしたら, 来なかったとすれば. The transformation therefore affects the final とする portion; the preceding content retains the information needed to express what is being assumed, its temporal reference, and whether it is affirmative or negative.

Grammatical dissection of とする

To understand the structure of とする, it is useful to separate the two elements that make it up. The construction contains the particle と, which delimits what the discourse is about, and the verb する, which retains the grammatical properties of a verb while taking on a meaning far more abstract than the ordinary “do”.

At this stage, we will not yet try to derive the meaning produced by their combination. Instead, we will examine what material can precede と, what function the particle performs, and what する contributes to the structure on its own.

The particle と: delimiting and presenting content

The と in とする is not the coordinating particle that can be translated as “and”, nor the particle that marks the person with whom an action is performed. It is the so-called quotative と or quotation particle.

The term “quotation”, however, must be understood in a grammatical sense, not merely as the reproduction of words someone has actually spoken. と can introduce a genuine direct quotation:

「明日戻る」と言った。

He said, “I’ll be back tomorrow.”

But it can also delimit the content of a thought, perception, or judgment without those words ever actually having been spoken:

彼が正しいと考えた。

I thought he was right.

In both cases, と draws a boundary after the preceding content and links it to a predicate that says something about that content. What comes before と is therefore treated as a recognizable unit: something that can be said, thought, believed, observed, evaluated, or discussed.

The difference becomes clear when we compare an independent proposition with the same proposition followed by と:

価格は一定である。

The price is constant.

価格は一定であると考える。

The price is considered to be constant.

In the first example, 価格は一定である constitutes the speaker’s main assertion. In the second, the same proposition is no longer presented as an independent statement: と delimits it and syntactically turns it into the content on which the following verb operates.

This shift is sometimes described as the “objectification” of content. This does not mean that と presents the information as objectively true. It means that it places the content at a certain distance, as a linguistic object that can be reported or subjected to a mental operation.

The particle by itself does not establish whether the content is true, false, certain, possible, or purely imagined: that interpretation depends on the predicate that follows and on the context.

It is equally important not to define と as a nominalizing element. Strictly speaking, the particle does not turn the proposition into a noun: the proposition retains its internal structure, and the predicate keeps its normal plain form. The copula だ also remains before と when the predicate is a noun or a な-adjective:

彼は医師だと聞いた。

I heard that he is a doctor.

その場所は静かだと感じた。

The place felt quiet to me.

The material delimited by と does not necessarily have to be a complete proposition. It can also be a noun indicating a designation, category, role, or state assigned to something:

この数をゼロと定める。

This number is defined as zero.

田中氏を代表と呼ぶ。

Mr. Tanaka is referred to as the representative.

In these cases, ゼロ and 代表 do not reproduce a spoken sentence. They represent, respectively, the value and role assigned to the element marked by を. Once again, と delimits a representation—“zero”, “representative”—and hands it over to the following predicate without itself expressing the act of establishing, naming, or recognizing.

The independent contribution of と can therefore be described through three closely connected operations: it delimits the preceding material, presents it as content or qualification, and links it to a predicate that will operate on it.

The verb する

In its most concrete lexical use, する indicates the performance of an activity:

宿題をする。

Do homework.

In the する we are analyzing, by contrast, the idea of a concrete action is greatly weakened. It does not describe someone physically “doing” or “making” an object or activity. For this reason, grammatical literature treats する in constructions of this kind as a formal verb (形式動詞): a verb whose lexical meaning is reduced and whose primary role is to provide the structure with a verbal predicate.

“Formal” does not mean useless or completely devoid of content. First of all, する retains all the morphological properties of a verb. It is in fact the element that can carry negation, tense, and politeness:

する　→　しない　→　した　→　します

Non-past form → negative form → past form → polite form.

It is therefore する that carries tense, negation, and politeness for the construction. The particle と remains unchanged; grammatical changes are expressed on the verb.

Moreover, する retains an abstract agentive component. Even when it does not describe a physical action, it normally presupposes an agent responsible for the operation: someone judges, establishes, assigns, adopts, or presents a particular content. That source can be expressed:

委員会はこの案を妥当とした。

The committee judged this proposal to be valid.

Here 委員会, “the committee”, is the subject of した. The verb does not indicate a concrete act of “doing”, but it retains the idea of an operation attributable to a responsible subject.

Very often, however, the subject of する remains implicit, especially in scientific, technical, legal, or regulatory texts:

本稿では、価格は一定であるとする。

In this study, the price is taken to be constant.

Within the content delimited by と, 価格は is the topic of 一定である. The source of the operation expressed by する, by contrast, is the author of the study or, more abstractly, the analytical model being adopted. The sentence therefore contains two distinct syntactic levels: the subject or topic internal to the content does not necessarily coincide with the subject—often omitted—of the external verb.

The omission of the latter contributes to the impersonal and formal character of the construction. The judgment is presented as part of the reasoning, rule, or method, while the person responsible for adopting it remains in the background. This does not mean, however, that the subject is grammatically nonexistent: it can be recovered from the context and, when necessary, expressed explicitly.

The abstract nature of する also explains why the same verb can appear in contexts involving evaluation, decision, classification, or the assignment of a value. There is no need to posit a completely different verb each time: the relatively unspecific lexical meaning of する allows it to provide a common verbal slot for different operations.

Considered separately from と, する therefore contributes three fundamental properties: it makes the structure verbal, supports its grammatical inflection, and introduces a source, expressed or implicit, responsible for the operation. How these properties interact with the content delimited by と belongs instead to the next stage of reconstruction.

Recombining とする

When the particle and the verb are brought back together, the fundamental shift becomes clear: content is presented and, through the verb, adopted in a particular way. と delimits what precedes it; する allows that content to become the object of an operation of judgment or framing. For the uses we are examining, we can represent this interaction pedagogically as “framing the matter in these terms”.

This is not a literal translation of the individual elements, but an interpretive key consistent with the continuity observed in the literature between presenting content, judging it, and determining it.

The hypothetical meaning emerges when this operation consists in adopting content as a premise for reasoning. Consider the difference:

参加者は十人だ。

There are ten participants.

参加者は十人だとする。

Suppose there are ten participants.

In the first sentence, the number of participants is directly asserted.

In the second, when read as setting up a hypothesis, the same content is adopted as a starting point: “for the reasoning we are carrying out, let us take it as given that there are ten participants”. The change therefore does not concern the content of the proposition, which remains the same, but the status that content receives in the discourse: from asserted information to adopted premise.

This is the use that the Daijisen describes with と仮定する, “to hypothesize that”.

Here we can see why simply translating する as “do” is unhelpful. No one is making the number of participants become ten, nor is anyone necessarily deciding how many people to admit. In the hypothetical interpretation, the operation concerns the reasoning: a situation is established as the one to be considered.

Likewise, と does not independently contain the meaning “suppose”: it presents the content on which the entire construction operates.

This reading leads to an essential distinction, already mentioned in the introduction: adopting something as a premise is not the same as considering it probably true. With 参加者は十人だと思う, “I think there are ten participants”, the speaker normally expresses a personal belief or assessment.

With hypothetical とする, by contrast, the speaker can adopt that number without taking a position on its reliability: it is simply needed in order to develop the reasoning. “Let us assume that this is so” does not necessarily mean “I believe that this is so”.

The hypothesis can even be explicitly incompatible with reality:

実際には摩擦があるが、この計算では摩擦はないとする。

In reality, friction exists, but in this calculation we assume that there is no friction.

The sentence does not claim that friction has disappeared, nor does it express uncertainty as to whether friction exists. It constructs an idealized situation within which the calculation can be performed. The example clearly illustrates the function of setting up a hypothetical scenario, distinct from the assertive or decisional uses of the same expression.

Naturally, the fact that a premise contrary to fact can be adopted does not mean that every premise introduced by とする is false.

This framing can also be expressed through a grammatically complete sentence followed by the consequences drawn from it:

参加者は十人だとする。一人に資料を二枚ずつ配るには、全部で二十枚必要になる。

Suppose there are ten participants. To distribute two sheets of material to each person, twenty sheets will be needed in total.

The first sentence establishes the premise; the second reasons within the situation thus outlined. とする does not already contain the consequence, nor does it necessarily have to connect that consequence within the same sentence: it can simply prepare the ground for what follows. Examples from linguistic research also document this independent use, in which the hypothesis is first formulated and then developed in the discourse.

Finally, we must avoid extending this reading to every occurrence of とする. Consider:

参加費を千円とする。

The participation fee is set at 1,000 yen.

In the context of an organizational decision, this sentence establishes an actual fee.

Within an illustrative calculation, by contrast, the same figure could be adopted only hypothetically. The structure shows continuity in how it functions, but the concrete value depends on what is being established and on the context: a decision and a hypothetical assumption are not the same operation.

The recomposition of the hypothetical use can therefore be stated in these terms: not “making content true”, but “adopting it as valid within the reasoning being constructed”. It is at this point that the presentation of the content and the operation expressed by the verb converge in the meaning “suppose that”, “assume that”, “let us posit that”.

Compositionality vs. idiomaticity: how transparent is とする?

After breaking down and recombining とする, we can now clarify to what extent its meaning can be derived from its components.

By “compositionality” here, we mean the possibility of understanding the whole through the recognizable contribution of its parts; by “idiomaticity”, we mean the weight of conventionalized uses that cannot be predicted simply by translating each element. In とする, these two aspects coexist: the structure is analyzable, but its meaning does not arise from the sum of two translations.

Its transparency concerns first and foremost its grammatical organization. We can still recognize content presented through と and linked to a predicate. An analysis of the particle makes it possible precisely to identify this continuity between quotative uses and uses that present content without reproducing words that were actually spoken.

We are therefore not dealing with a sequence whose parts have lost every comprehensible relation to the way the whole functions.

This organization remains visible even when the content of the hypothesis changes:

この町に駅があるとする。

Suppose there is a station in this town.

この町に駅がないとする。

Suppose there is no station in this town.

The shift from ある to ない changes the situation being assumed, not the operation of assuming it: in the second example, the hypothesis concerns an absence; it is not the act of hypothesizing itself that is negated.

The sentence is therefore not a completely frozen formula. The construction provides a pattern into which different contents can be inserted while preserving the hypothetical value also recognized by dictionaries.

This transparency, however, does not make the meaning automatically predictable from the most elementary senses of the components. Knowing that と can mark a quotation and that する can mean “do” is not enough to arrive at “suppose that”.

One must also know the abstract functioning of the verb and the value acquired by the combination. Understanding why a meaning is motivated is not the same as being able to freely invent it from its components.

This is where the conventional dimension comes in. In its hypothetical use, とする is an established way in Japanese of introducing an assumed situation. There is no need to assign the meaning “hypothesis” separately to と or to turn する into a general synonym for “hypothesize”: that value belongs to the construction in this specific use.

The concept of grammaticalization is useful for describing this situation: the development of grammatical functions from elements that have lexical meaning. In one study, Ōtsuka specifically emphasizes the weakening of the concrete meaning of する and observes that the degree of grammaticalization varies across its different uses.

This points the analysis toward a construction with an abstract function, rather than toward a simple figurative expression in which “do” must be interpreted through an occasional metaphor.

We must also distinguish the stability of the construction from the idea that it has a single meaning. Recognizing とする does not mean that we can translate it as “hypothesize” every time. Studies distinguish, among others, hypothetical, declarative, decisional, and descriptive uses; to identify them, they consider sentence structure, context, and possible paraphrases.

The shared logic helps connect these uses, but it does not erase the distinctions that Japanese maintains between them.

The recomposition discussed in the previous section must also be read within this limitation. “Adopting content as a premise” is an explanation of how the hypothetical use works, not a word-for-word translation.

And a semantically convincing reconstruction does not, by itself, constitute proof of the historical origin of the construction: explaining how the components contribute to the present-day meaning is a different task from documenting when and through what stages that use developed.

The contrast between compositionality and idiomaticity, then, does not require an absolute choice. For とする, we can speak of a grammatically motivated construction that is conventionalized in use: dissection makes its organization intelligible, while knowledge of actual usage allows it to be interpreted correctly. Transparent does not mean literally translatable; conventional does not mean resistant to analysis.

Register and contexts of use: とする, とすると, とすれば, and としたら

The fact that these expressions are used to set up hypotheses and lines of reasoning does not mean that they all belong to a rigidly formal register.

Their naturalness also depends on the communicative activity: formulating a premise, discussing a possibility, drawing a consequence, or inviting someone to imagine a situation. It is therefore more useful to observe how they are used in discourse than to place them on a fixed scale from “more formal” to “more conversational”.

とする, when it closes a sentence that establishes an assumption, is particularly natural in mathematical problems, technical explanations, and texts that need to define the conditions for the reasoning clearly.

計算上、一か月を三十日とする。

For the purposes of the calculation, we assume that a month has thirty days.

The formulation presents the premise compactly, without dwelling on the personal involvement of the person proposing it. Grammatical descriptions illustrate this use precisely through problems, calculations, and situations adopted as starting points.

This expository character does not exclude spoken language. During an explanation, a teacher can say 一か月を三十日とします, “we assume that a month has thirty days”, preserving the same framing while adopting the polite register. The distinction between written and spoken language does not, in fact, coincide with the distinction between formal discourse and spontaneous conversation: an oral presentation can also have a reasoning structure similar to that of written discourse.

Ōtsuka explicitly draws attention to this distinction when describing the uses of とする.

By contrast, とすると can fit very naturally into everyday interaction. The form lends itself to taking a piece of information into consideration and evaluating its consequences: travel time, the number of guests, an expected expense, or information that has just been received.

駅まで二十分かかるとすると、もう出ないと間に合わないね。

If it takes twenty minutes to get to the station, we need to leave now if we want to make it in time.

The analytical tone does not make the sentence bookish: here it accompanies a practical assessment shared with the listener. The same form can appear in a technical exposition, but it is not the scientific content that makes it appropriate; it is the transition from premise to the evaluation that follows. From this perspective, とすると can be described as an expression that provides a framework within which the reasoning can continue.

とすれば works well in discussions where the validity and implications of a hypothesis are being examined. It can accompany an analysis, a professional assessment, a reconstruction of events, or an objection:

この見積もりが正しいとすれば、予算内に収まるはずです。

If this estimate is correct, we should be able to stay within budget.

Here the conclusion is presented as dependent on accepting the estimate. This way of proceeding can give the discourse a measured, analytical tone, but it does not make とすれば an exclusively written form: friends can also compare explanations, discuss clues, or test a line of reasoning. It should therefore not be regarded simply as the “more elegant” substitute for としたら.

としたら shows a stronger affinity with conversation, especially when the hypothesis frames a scenario involving wishes, preferences, evaluations, or questions directed at the other person:

一週間休みが取れるとしたら、何をしたい？

If you could take a week off, what would you like to do?

The listener is invited to imagine themselves in the situation and give a personal response. This openness makes としたら particularly suitable for conversations about future possibilities, exploratory questions, and imaginary scenarios. Its greater affinity with spoken language is also noted in grammatical descriptions, but it should be understood as a tendency, not as a restriction to spoken language.

Above all, conversational does not mean impolite. としたら can be used perfectly naturally in a professional question formulated with the appropriate degree of politeness:

この案を修正するとしたら、どこを変えるのがよいでしょうか。

If we were to revise this proposal, what would be best to change?

The overall tone also depends on the vocabulary, the wording of the question, and the ending でしょうか. There is no need to replace としたら automatically with とすれば simply in order to address someone politely.

The Japan Foundation also uses としたら in polite questions addressed to the reader in explanatory texts. This provides concrete evidence that affinity with spoken interaction, politeness, and written medium are separate dimensions.

In dialogue or conversation, moreover, these forms can pick up what has just been said through openings such as だとすると, そうだとすれば, and そうだとしたら: “if that is so”, “if things are like that”. Studies of discourse document precisely this linking function between preceding information and the next turn.

They are not used only to build isolated hypotheses, but also to move a conversation forward.

The choice, then, is not only about how formal we want to sound. What matters above all is whether we are setting up a premise, developing a consequence, or involving the listener in a scenario. Register preferences interact with these functions without determining them: the four forms are not merely stylistic variants that can be freely interchanged.

Usage examples

とする

この計算では、温度は一定としよう。

ここに、誰も住んでいない家が一軒あるとする。

毎月の収入を二十五万円とする。

とすると

片道に二時間かかるとすると、往復だけで四時間必要になる。

この話が本当だとすると、予定を見直す必要がある。

鍵がここにないとすると、どこに置いたんだろう。

とすれば

この報告書に問題があるとすれば、根拠となるデータが少ないことだ。

彼が本当に何も知らなかったとすれば、あの反応も理解できる。

来年も同じペースで売り上げが伸びるとすれば、目標の達成は十分可能だ。

としたら

生まれ変われるとしたら、どんな人生を送りたい？

海外に引っ越すとしたら、まず言葉の問題が心配だ。

私の言葉であなたを傷つけたとしたら、本当にごめんなさい。

Conclusions

Understanding とする means recognizing a fundamental step in discourse: propositional content is adopted as a starting point for reasoning.

In the hypothetical use examined here, this is the core that links the basic form to とすると, とすれば, and としたら. The differences between these expressions make sense when we look at how the speaker introduces the premise and what they intend to derive from it: a conclusion, a question, an evaluation of the imagined situation. The English translation is the result of this analysis, not its starting point.

To consolidate what has been learned, a useful exercise could be to collect examples accompanied by at least some context.

For each sentence, note two things: what content is being assumed and how the reasoning continues. When the premise picks up information from an earlier statement, it is worth keeping that earlier line or sentence as well. In this way, the grammatical forms remain connected to the communicative situation that clarifies their use.

Comparing variants can also be instructive, provided it does not turn into automatic substitution.

Starting with a reliable example, you can try changing only とすると, とすれば, or としたら and then check the result with a teacher: does the sentence remain natural? Does the nuance change? Does what follows also need to be modified? The aim of the exercise is to learn how to justify a choice without expecting every context to allow only one solution.

One final practical point concerns the volitional form encountered in the examples: ～としよう and ～ようとする are not the same construction. In the first case, it is する that becomes しよう and, in the use studied here, the meaning is “let us suppose that…”. In the second, the volitional form belongs to the verb preceding と: the construction can express an attempt or the imminence of an event.

Paying attention to where the inflection occurs therefore helps prevent confusion between structures that look very similar.

This attention to structure also provides a solid foundation for approaching として, としては, and としても without automatically assigning the meaning “to hypothesize” to all of them. Each requires us to identify the construction and its actual use. This is precisely the value of grammatical dissection: turning a familiar sequence into an intelligible linguistic choice.

References

• Nakayama, Eiji (2001). 仮定的な事態をさしだす「～とする」とその周辺. 人間文化学研究集録, 10, 21–32.
• Iwao, Takanori (2007). 「とする」構文についての覚書. 日本語・日本文化, 33, 1–16.
• Ōtsuka, Nozomi (2016). 「～とする」における引用と決定・同定の連続性：「～と言う」と比較して. 日本語日本文学, 26, 39–54.
• Niwa, Saburō. 日本語文法概説: §40.6, ～とする and §49.8, ～とすると／すれば／したら／しても.
• Tokyo University of Foreign Studies. Japanese Grammar Module: case particles and quotative と, volitional form, and conditional forms.
• The Japan Foundation (2006). 文法を楽しく「は」と「が」: part 1 and part 2.