9.2 ～たら conditional

～たら expresses a situation where A happens first, and then B follows. Depending on context, it can mean “when / after” or “if”.

Formation

～たら is formed from the past form.

Plain form

Verbs

• たべる食べる → たべたら食べたら
• いく行く → いったら行ったら

い-adjectives

• たかい高い → たかかったら高かったら
• いそがしい忙しい → いそがしかったら忙しかったら

な-adjectives / nouns Use だったら.

• しずか静か → しずか静かだったら
• がくせい学生 → がくせい学生だったら

Polite forms (です・ます)

In polite speech, です / ます change to でした, then ～たら is added.

• たべます食べます → たべましたら食べましたら
• しずか静かです → しずか静かでしたら
• がくせい学生です → がくせい学生でしたら

This applies to verbs, な-adjectives and nouns (not い-adjectives).

Negative form

Form the past negative, then add ～たら.

Verbs

• いかない行かない → いかなかったら行かなかったら

い-adjectives

• たかくない高くない → たかくなかったら高くなかったら

な-adjectives / nouns

• しずか静かじゃない → しずか静かじゃなかったら
• がくせい学生じゃない → がくせい学生じゃなかったら

Usage

When / after something happens

～たら often means “when” or “after”. The first action must finish before the next one starts.

This is similar to using ～てから.

When ～たら is used with ～ている (～ていたら), the nuance changes slightly. Instead of focusing on completion, it describes a situation that is ongoing at the time something happens.

In this use, ～ていたら often means “while doing A” or “in the middle of A”, rather than “after A.”

When describing past events, ～たら requires that B was an unexpected discovery or unplanned result — not a deliberate action that followed A by plan. For deliberate past sequences, use ～てから instead: 食べ終わってから歯を磨いた. In future contexts, ～たら has no such restriction:

If something happens

～たら is also used as a natural “if”.

To clearly mark this as “if” (not “when”), もし or もしも is often used.

Counterfactual situations

～たら can also be used to talk about imagined alternatives to the past — situations that did not actually happen.

To clearly express regret or disappointment, ～のに is often added.

How about?

～たら works very well for suggestions, especially when reacting to a situation or what the other person just said.

--

Confirming assumptions

～たら is often used to confirm an assumption and then give a response based on it. This corresponds to expressions like “if that’s the case”, “if that’s what you mean”, or “if it’s what I’m thinking”.

The speaker first accepts the assumption as true, then continues with advice, information, or a conclusion.