Translation guide
The quality of being stupid, foolish, or lacking intelligence. In Japanese, this is expressed through nouns describing the trait, adjectives for describing people/actions, and verbs for acting stupidly. The most common and versatile word is 馬鹿 (baka), but many nuanced terms exist for different contexts.
stupidity (trait)
stupid action/idea
To refer to the abstract quality of being stupid, foolish, or unintelligent.
The most direct and neutral noun for 'stupidity' or 'foolishness'. Derived from the adjective 愚か (oroka). Suitable for both spoken and written contexts.
I'm amazed at his stupidity.
It's hard to admit one's own foolishness.
Noun form of 馬鹿 (baka), meaning 'stupidity' or 'idiocy'. More colloquial and emotionally charged than 愚かさ. Often used in casual speech.
A formal or literary term for 'stupidity' or 'dullness'. Implies a slow-witted, obtuse nature. Rare in everyday conversation.
To call someone stupid or refer to a stupid person. Note: Japanese often uses the same word for the trait and the person.
The most common word for 'stupid person' or 'idiot'. Can be used playfully or as a strong insult depending on tone. Also used as an adjective (馬鹿な).
To describe an action or behavior as stupid, foolish, or idiotic.
Pre-noun adjectival meaning 'absurd', 'ridiculous', or 'stupid'. Used to describe actions, ideas, or situations. Very common.
To describe the act of pretending to be stupid or deliberately acting foolishly.
English 'stupidity' is often used as a mass noun, but Japanese prefers specific constructions. For example, 'His stupidity surprised me' is better as 彼の愚かさに驚いた rather than a direct noun translation.
馬鹿 (baka) is standard Japanese and used nationwide. 阿呆 (aho) is strongly associated with the Kansai region. In Kansai, 阿呆 can be more playful, while 馬鹿 is harsher. In Tokyo, 馬鹿 is the default, and 阿呆 may sound dialectal or comedic.
馬鹿 can attach to nouns to mean 'absurdly' or 'stupidly', e.g., 馬鹿正直 (baka-shōjiki, 'honest to a fault'), 馬鹿力 (baka-jikara, 'brute strength'). This is a productive pattern in casual speech.
I can't believe his stupidity.
I can't deal with that level of stupidity.
彼の愚鈍さがプロジェクトの進行を妨げた。
His stupidity hindered the progress of the project.
That guy is really stupid.
Don't say stupid things.
Kansai-dialect equivalent of 馬鹿, but widely understood. Often used in comedy or friendly teasing. Can be more lighthearted than 馬鹿 in some regions.
What are you doing, you idiot!
A more formal or literary term for 'fool' or 'stupid person'. Less harsh than 馬鹿, but still negative. Often used in admonishments or storytelling.
You're a fool to do such a thing.
Means 'blockhead' or 'dunce', emphasizing clumsiness or lack of common sense. Often used for someone who makes silly mistakes.
He has a stupid look on his face.
That's a stupid idea.
I made a stupid mistake.
Adjectival form meaning 'foolish' or 'stupid'. More formal and less emotional than 馬鹿げた. Suitable for serious contexts.
It was a foolish act.
Means 'trivial', 'worthless', or 'stupid' in the sense of being pointless. Often used for silly jokes or meaningless tasks.
Don't get angry over such a stupid thing.
He played dumb and didn't answer the question.
A verb meaning 'to play dumb', 'to feign ignorance', or 'to act innocent'. Very common in casual conversation.
Don't play dumb, you know it, right?
Means 'to pretend not to know' or 'to ignore'. Often used when someone deliberately avoids acknowledging something.
He pretended not to know me even though he saw me.
That was a stupid mistake.