だった

だった and でした are the past tense forms of the copula だ and です, respectively. They are used to express that something was or used to be something. だった is the plain (casual) form, while でした is the polite form.

With nouns

Used to state what something or someone was in the past.

With な-adjectives

Used to describe a past quality or state using a な-adjective.

Negative past forms

The negative past forms are じゃなかった (casual) and じゃありませんでした / ではありませんでした (polite).

Usage notes

• だった is used in casual conversation, inner thoughts, and plain-form contexts such as subordinate clauses.
• でした is used in polite speech and formal situations.
• い-adjectives do not use だった / でした for their past tense. Instead, they use their own conjugation (e.g. たかい高い → たかかった高かった / たかかったです高かったです). Using だった with い-adjectives (e.g. ×高いだった) is a common mistake.