When adjectives are not immediately succeeded byです or any of its conjugated forms (だ, でした), it needs to conjugated according to its intended usage. To conjugate an い-Adjective into its past-tense, simply replace the い at the end with かった.
楽しかった – was fun
おいしかった – was delicious
面白かった – was interesting
*The irregular adjective to this construct is いい, which reverts back to its original form of よい before becoming よかった to mean “was good”.
い-Adjectives (Negative Past Tense):
To conjugate an い-Adjective into its negative past-tense, simply replace the い at the end withくなかった (です), or, くありませんでした for more formality.
楽しくなかった – was not fun
おいしくなかった – was not delicious
面白くなかった – was not interesting
When two or more い-adjectives are used together to describe the same entity, it is only the finally listed adjective that is conjugated according to usage; all prior adjectives are conjugated into the て Form, which is derived by replacing the い at the end of the い-adjective withくて.
面白くて楽しかった – was interesting and fun
大きくてうるさい – big and loud
When we mean to connect い-adjectives that are in their negative conjugation, we change the くないto くなくて.
楽しくなくてつまらない – not fun and boring
優しくなくてひどい – not nice and awful