だった・でしたWas, Were (Past tense)

だった・でした and だ are all used to assert or identify something. The difference among them is in formality and tense. だ is casual and present tense (similar to the English 'is'/'am'), while だった・でした is past tense ('was'), with だった being casual (the past tense of だ) and でした being polite (the past tense of です).

The past form of う-Verbs expresses a completed action or an event that took place in the past, similar to the English '-ed.' In contrast, だった and でした are used after nouns to express the past tense, indicating that something 'was' or 'were' in a certain state. While the meaning (something happened or existed in the past) is the same, the grammatical expression differs depending on the word type (verb vs. noun).

です and だった・でした are all forms of 'is' or 'to be,' but they show different tenses. です is used for the present or future, like in あれは猫です ('That is a cat'). だった and でした are past tense—だった is casual, and でした is polite. For example, あれは猫だった means 'That was a cat.'