〜としたら / 〜とすれば
Supposing 〜としたら
Meaning
"Supposing ~", "if we assume ~" — reasoning from a hypothetical.
Formation
[plain form] + としたら / とすれば / とすると
Notes
For working through a supposition rather than a real condition, so it pairs with 何, どう, どこ: 宝くじが当たったとしたら何を買いますか. The second clause is a judgement or question, never a command.
Examples
宝（たから）くじが当（あ）たったとしたら、何（なに）を買（か）いますか。
Supposing you won the lottery, what would you buy?
Breakdown
今（いま）から行（い）くとすれば、何時（なんじ）に着（つ）きますか。
If we set off now, what time would we arrive?
Breakdown
彼（かれ）の話（はなし）が本当（ほんとう）だとしたら、大変（たいへん）なことです。
If his story is true, this is serious.
Breakdown
一日（いちにち）休（やす）めるとしたら、どこへ行（い）きたいですか。
If you could take a day off, where would you want to go?
Breakdown
この値段（ねだん）だとすると、少（すこ）し高（たか）すぎます。
If that is the price, it is rather too expensive.
Breakdown
⚠️ Often confused with
〜と、〜
Conditional と (whenever / when)
Two uses: (1) natural/habitual consequence — "whenever A happens, B happens"; (2) discover...
〜ば
Conditional 〜ば (if / whenever)
A general conditional — "if A, then B". Formed from the hypothetical form (仮定形) of the...
〜たら
Conditional 〜たら (if / when / after)
The most versatile conditional. "If/when A happens, B". Formed from the ta-form stem + ら....
〜なら
Conditional 〜なら (if / given that)
A conditional based on the listener's stated or known information — "if it's the case that...
〜ても / 〜でも
Even if 〜ても
"Even if A, B" / "no matter if A". Indicates that B happens regardless of A. The result is...
〜場合は
In case 〜場合は
"In the event that ~ / in the case that ~". Used to discuss what to do in a particular (of...
〜ないことには
Unless 〜ないことには
"Unless ~", "without first ~ing" — nothing can proceed until this happens.
〜てからでないと
Not until 〜てからでないと
"Not until ~", "unless ~ is done first" — a precondition that must come first.
〜さえ〜ば
If only 〜さえ〜ば
"If only ~", "as long as just ~" — one sufficient condition.