～とする (1) (to assume / to suppose)

Japanese Grammar Intermediate Japanese ★★★★ 4/5 neutral とするto suru
Reading とする
Romaji to suru
Formation Sentence (plain form) + とする / Noun + とする / A を B とする

Meaning

A phrase indicating that someone assumes, supposes, or tentatively decides something for the sake of argument or planning. It conveys 'let's assume that' or 'supposing that.'

とする in this usage frames a hypothetical premise for reasoning, planning, or discussion. It is extremely common in academic writing, presentations, and logical arguments. The forms としたら, とすれば, and とすると are conditional extensions meaning 'if we assume that.' としても means 'even assuming that.' This pattern is distinct from とする meaning 'to attempt' or 'to feel,' which are separate grammar points. In formal writing, AをBとする is used to define terms or assign roles.

Examples

  1. 仮に彼の言っていることが正しいとすると、計画を変えなければならない。 Assuming what he says is correct, we will have to change the plan.
  2. 一人当たりの費用を五千円とすると、全体で十万円になる。 If we assume the cost per person is five thousand yen, the total comes to one hundred thousand yen.
  3. 彼女をリーダーとする新しいチームが結成された。 A new team was formed with her as the leader.

Usage Guide

Context: spoken, written, academic, business

Tone: analytical

Do Say

  • 予算が半分に削られたとすれば、何を優先すべきか考えよう。
  • 一日に二時間勉強するとして、全範囲を終えるのに三週間かかる。
  • 田中さんを議長とする委員会が設置された。
  • もしこの計画が失敗したとしても、得られる経験は大きい。

Don't Say

  • 明日雨が降るとする。(Sounds like dictating reality rather than hypothesizing; add 仮に or としたら to clarify the hypothetical intent) → 仮に明日雨が降るとしたら、イベントは中止だ。
  • 彼は学生とする。(Ambiguous — could mean 'assume he is a student' or 'make him a student'; context or additional markers like 仮に are needed) → 仮に彼が学生だとすると、学割が使える。

Origin & History

Combines the quotative particle と with する (to do/make). The construction literally means 'to make it that' or 'to treat it as,' and has been used since classical Japanese to frame hypothetical premises.

Cultural Context

Generation: All ages

Social background: Universal

Related Phrases

～も～も (both ~ and ~ / neither ~ nor ~) A structure presenting two states or actions of someone or something by using the inclusive particle も twice to emphasise that both apply equally. It conveys 'both ~ and ~' or with negation 'neither ~ nor ~.' ～より (more than / comparative) An adverb and particle that forms the comparative degree of adjectives and adverbs, expressing 'more ~ than' or 'rather than.' It establishes a standard of comparison. ～ことになる (it turns out that) A phrase indicating that an action or event leads to a certain situation or outcome, often implying that the result was decided by external circumstances rather than the speaker's own will. It conveys 'it turns out that' or 'it has been decided that.' ～そうになる (to almost / to nearly) A phrase expressing that something almost happens or nearly occurred. It describes a situation that was on the verge of happening but ultimately did not, conveying 'almost' or 'nearly.' ～とする (2) (to feel / to sense) A phrase describing a sensory or psychological experience, where the speaker perceives a physical sensation or emotional state. It conveys 'to feel' or 'to have a sensation of.' ～もの（だ） (it is natural that / used to) A dependent noun construction used to express general truths, natural expectations, nostalgic recollections of the past, or emotional emphasis. It conveys 'it is natural that,' 'one should,' or 'used to.' ～やる (1) (to do for / to give) A verb meaning to cause something or someone to move to a place, or to do, give, eat, or drink something. It is a casual or rough equivalent of あげる for giving to animals, plants, or those of lower status, and also functions as a general verb for 'to do.' ～よう (conjecture / likelihood) An auxiliary verb attached to the volitional stem expressing the speaker's conjecture about some potentiality or likelihood. It conveys 'it seems likely that' or 'it appears that ~ will.'
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