合う【あう】

The suffix あう合う (あう) is attached to the masu-stem of a verb to express that an action is done mutually, reciprocally, or together. It conveys the idea of "doing something to/with each other" or "doing something for one another."

Structure

Take the masu-stem of a verb and add あう合う:

• はなす話す → 話し → 話し合う (to discuss / talk with each other)
• たすける助ける → 助け → 助け合う (to help each other)
• おしえる教える → 教え → 教え合う (to teach each other)

The resulting compound verb conjugates as a regular godan (う) verb: 話し合う → 話し合います → 話し合った → 話し合わない.

Reciprocal actions

The most common use of ～合う is to describe two or more people performing the same action toward each other.

The subject is often marked with と to indicate the other party involved in the mutual action.

Doing something together

～合う can also emphasize that people are doing something jointly or collectively, even when the action is not strictly reciprocal.

Common compound verbs with 合う

Some ～合う compounds have become fixed expressions with their own nuanced meanings:

• しりあう知り合う – to get to know each other; to become acquainted
• つきあう付き合う – to go out with (someone); to associate with
• はなしあう話し合う – to discuss; to talk things over
• むきあう向き合う – to face each other; to confront

Some of these fixed compounds have developed meanings beyond simple reciprocity, so it is worth learning them individually.