Translation guide
How to express that something works, produces results, or is in effect in Japanese.
Say that a method, medicine, or action works or is successful.
Say that a law, rule, or agreement is currently valid or applicable.
Used for tickets, contracts, laws, etc. that are valid or in effect.
この切符は明日まで有効です。
This ticket is effective until tomorrow.
その法律はまだ有効だ。
That law is still in effect.
Say that a tool, machine, or system works properly.
Means 'to function'. Neutral for machines, systems, or organizations.
このシステムは正常に機能している。
This system is functioning effectively.
効く is a casual verb often used for medicine or immediate effects. 効果がある is a general phrase meaning 'has an effect', suitable for most situations. 有効 is more formal and often used for validity of tickets, laws, or strategies.
薬が効く。
The medicine works.
運動は健康に効果がある。
Exercise is effective for health.
このパスワードは有効です。
This password is valid.
That method didn't work at all.
Literally 'has an effect'. Neutral and widely used for anything from medicine to policies.
この運動はダイエットに効果がある。
This exercise is effective for dieting.
Means 'valid' or 'effective'. Often used for measures, strategies, or official things. Slightly formal.
この対策は有効だ。
This measure is effective.
Similar to 効果がある but more colloquial. Often used for medicine or immediate results.
この薬はすぐに効き目がある。
This medicine takes effect quickly.
Literally 'has legal force'. Used for contracts, laws, or official documents.
この契約はまだ効力がある。
This contract is still effective.
Can sometimes be used for rules or threats, but mainly for physical effects. Use with caution.
Not the primary choice for legal validity; 有効 is safer.
その脅しは彼には効かない。
That threat isn't effective on him.
Means 'to be useful'. More about practical utility than technical function.
このアプリは本当に役に立つ。
This app is really effective.