What it means
決して〇〇ない emphasizes a strong negative meaning: “never,” “not ever,” or “by no means.” It is normally used with a negative predicate and often expresses the speaker’s firm determination, denial, or certainty that something does not happen. The pattern can describe actions, qualities, states, and identities. In polite sentences, the predicate changes to its polite negative form, while 決して remains unchanged.
Usage note
決して is stronger and more emphatic than an ordinary negative sentence. Do not use it with an affirmative predicate. For a simple statement that something has not happened, a less emphatic negative form is usually more natural.
How to use it
彼は決して医者ではありません。
He is by no means a doctor.
この部屋は決して静かではありません。
This room is by no means quiet.
この薬は決して苦くありません。
This medicine is by no means bitter.
私は決して約束を忘れません。
I will never forget the promise.
彼は決して医者ではない。
He is by no means a doctor.
この部屋は決して静かではない。
This room is by no means quiet.
この薬は決して苦くない。
This medicine is by no means bitter.
私は決して約束を忘れない。
I will never forget the promise.