Translation guide
The English word "act" covers a wide range of meanings, from taking action to performing in a play, behaving in a certain way, or serving a function. This guide breaks down the main uses and provides natural Japanese equivalents for each.
To do something, especially in response to a situation or to achieve a result.
The most general and common way to say "act" in the sense of taking action. It implies moving or behaving with a purpose.
We need to act immediately.
He acted rather than just talking.
Literally "to move," often used when someone finally takes action or when a group/organization starts doing something.
To take measures or countermeasures; used when acting to solve a problem.
To behave or conduct oneself, often with an adverb describing the manner.
To perform a role in a dramatic production.
To play a role; the standard verb for acting in theater, film, or TV.
To behave as if something is true when it is not; to fake an emotion or role.
The most common way to say "pretend" or "act like." Used with verbs or adjectives.
To fulfill a purpose or role, often for objects or systems.
To function as; used for machines, systems, or abstract things.
To start working or become operative.
To be effective; used for medicine, poison, magic, etc.
A thing done; an act as a countable noun.
A general term for an act or deed, often used in formal or legal contexts.
A major section of a theatrical work.
Act of a play; also used metaphorically for stages of life.
行動する focuses on taking concrete actions, while 振る舞う describes the manner of behavior or conduct. Use 行動する for "act decisively" and 振る舞う for "act politely/rudely."
He acted bravely (took brave actions).
Stop acting like a child.
警察はまだ動いていない。
The police haven't acted yet.
The government should act quickly.
Describes how someone behaves, especially in social situations. Can be positive or negative.
He acted like a gentleman.
The children were acting politely.
Also used for behaving, but more focused on actions than mannerisms.
He acted strangely.
Pattern: "act like a ~"
She acts like a queen.
He acted Hamlet.
She acts the lead role in that movie.
To perform acting; emphasizes the craft of acting itself.
He acts very naturally.
To appear in a production; focuses on being in the cast rather than the performance.
She will act in next month's play.
He acted sick.
Don't act like you don't know.
To feign or pretend, often used for emotions or states. Slightly more formal/literary.
She acted calm.
Can also mean to put on an act in real life, implying insincerity.
His sadness was just an act.
This device acts as a sensor.
To work or act in a certain way, often for forces or influences.
Gravity acts as a brake.
To play a role; emphasizes fulfilling a function or duty.
Education acts an important role.
この薬はすぐに効く。
This medicine acts quickly.
To act on something; more technical, used in science or formal contexts.
This chemical acts on the nerves.
To come into effect (for laws, treaties).
The new law will act next month.
That is a criminal act.
I appreciate his kind act.
Action or behavior; more about the process than a single deed.
I can't understand his acts.
A deed, often with a nuance of mischief or blame. "The work of..."
Whose act is this?
The second act begins.
彼は勇敢に振る舞った。
He acted bravely (behaved in a brave manner).
English often uses "act" as a noun where Japanese prefers a verb phrase. For example, "an act of kindness" is more naturally 親切な行為, but in many cases rephrasing with a verb is better.
The drug acts on the brain.