い-adjectives (affirmative past tense)

About

い-adjectives can be turned into the past tense by turning their final い kana into 「かった」. There are no exceptions to this rule, although many people forget that the past tense of the い-adjective いい ("good") is よかった.

The past tense of an い-adjective is considered casual, or plain form, and therefore indicates casual speech when ending a sentence on its own. To make it more polite, です may be directly attached. However, keep in mind that when attached to a past tense い-adjective, です must remain in the present tense to avoid having two past tense markers. い-adjectives may not be directly followed by だ, in any tense.

The past tense of い-adjectives may also attach to nouns, to indicate a past quality of said noun (e.g. 「おいしかった料理りょうり」"cooking that was delicious").

Summary

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  To change an い-adjective to the past tense, replace the final い with かった.

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  Past tense い-adjectives can be made polite using です.

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  Past tense い-adjectives can't be directly followed by だ.

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  Past tense い-adjectives can also modify nouns.