としたら・
These forms explicitly ask the listener or reader to assume a situation temporarily, then consider what would follow. The assumption may be realistic, unlikely, or contrary to fact.
Reasoning from an assumption
The clause before the target is treated as a temporary premise. The rest of the sentence can give a calculation, judgment, plan, inference, or question based on that premise. The form does not by itself tell you how likely the premise is; the surrounding context must make that clear.
Calculations and imagined cases
参加者が三十人だとすると、一部屋に十人ずつ泊まるには三部屋必要だ。
Assuming there are thirty participants, we will need three rooms if ten people stay in each room.
AnalyzeThe number of participants is used as the premise for a planning calculation.
もし一週間自由だとしたら、どこへ行きたいですか。
If you had a whole week free, where would you like to go?
AnalyzeThis conversational question invites the listener to imagine a situation.
現実には考えにくいが、人間が百五十歳まで生きられるとすれば、働き方も大きく変わるだろう。
It is hard to imagine in reality, but if humans could live to the age of 150, the way people work would also change greatly.
AnalyzeThe opening words clearly mark the premise as unlikely.
Drawing an inference
窓が内側から壊されたとすると、犯人は建物の中にいたことになる。
If we assume the window was broken from the inside, it follows that the culprit was inside the building.
Analyzeとすると is particularly natural when the next clause presents a logical consequence.
Choosing among the three forms
Swipe sideways to compare every column.
| Form | Common tendency |
|---|---|
| としたら | Often used when personally imagining a case, especially in conversation. |
| とすれば | Often suits careful reasoning, judgments, and planning. |
| とすると | Readily leads from an assumption to a calculation or inference. |
These are preferences, not strict divisions. The forms overlap considerably, so context and style matter more than a rigid one-to-one rule.
Assuming a situation versus it becoming established
だとしたら presents the overseas assignment as a premise for discussion. By contrast, となったら contains the idea of becoming and foregrounds the assignment actually being decided or established.
More examples
この数字が正しいとすると、予算はあと二百万円足りない。
Assuming these figures are correct, the budget is still two million yen short.
Analyze彼が本当に知らなかったとしたら、あの反応も理解できる。
If he really did not know, that reaction is understandable too.
Analyze全員が参加するとすれば、もっと広い会場を予約すべきだ。
If we assume everyone will attend, we should reserve a larger venue.
Analyzeその話が事実だとしたら、なぜ今まで公表されなかったのだろう。
If that story is true, why was it not made public until now?
Analyzeあなたが責任者だとすると、最初に何を変えますか。
Assuming you were in charge, what would you change first?
Analyze仮に海面が一メートル上がるとすると、この地域にも影響が出る。
Suppose sea level were to rise by one meter; this area would also be affected.
Analyze