Reviewing Japanese tense and negation across four predicate types

Choose the predicate type before time and polarity

Do not treat every ending as a change from です to でした. Identify a verb, i-adjective, na-adjective, or noun predicate first; choose non-past or past and affirmative or negative next; then keep the sentence style consistent. Initially change only those two dimensions rather than also changing the subject, vocabulary, and pattern.

きれい ends in the kana い but is a na-adjective. 好き is also a na-adjective. 高い and 寒い belong to the i-adjective group. Check the book or dictionary when the category is uncertain instead of guessing from characters or the final kana. This guide starts with independent sentence predicates; noun modification, quotation, and subordinate clauses have their own connection rules.

Use a grid for polite endings

This grid is arranged for this guide. Read across to change time and polarity, and down to separate the four predicate types. Cover the final three columns and recall the forms before checking and using them in a meaningful sentence. I-adjective negatives also allow 高くありません and 高くありませんでした; the grid uses 高くないです and 高くなかったです without implying that they are the only correct options.

Na-adjective and noun negatives also appear with conversational forms such as じゃありません and じゃないです. Start with one coherent set, then record alternatives with their contexts rather than trying every variant in the same practice round.

Keep plain forms separate; do not add だ mechanically

For 読む, the four forms are 読む, 読まない, 読んだ, and 読まなかった. Learn the verb group’s nai-form and ta-form, then form past negatives with ない to なかった. 食べる gives 食べない, 食べた, 食べなかった; する gives しない, した, しなかった; 来る gives 来ない（こない）, 来た（きた）, 来なかった（こなかった）. The plain negative of ある is ない, not あらない.

For the i-adjective 高い, use 高い, 高くない, 高かった, 高くなかった without だ. いい changes through よい: よくない, よかった, よくなかった. The na-adjective きれい uses きれいだ, きれいではない, きれいだった, きれいではなかった. A noun such as 学生 takes だ, ではない, だった, and ではなかった as an independent predicate too. Conversational じゃない and じゃなかった are variants of those negatives.

Non-past is not only present; past can describe a state

The basic contrast is non-past versus past, interpreted with time expressions and context. 毎朝、本を読みます describes a habit; 明日、本を読みます describes a future arrangement. Reading in progress normally needs an expression such as 本を読んでいます rather than translating every ます as “right now.” ている also has other uses, beyond the scope of this focused comparison.

Past forms can describe an action in 昨日、本を読みました or a state in 昨日は寒かったです. A past negative is not made by attaching でした to every present negative: verbs use ませんでした, and i-adjectives use forms such as くなかったです. Ask whether the statement or action was true at that time before selecting polarity.

Locate a category, form, or context error

Change 高いでした to 高かったです: an i-adjective was treated like a です predicate. Change きれくなかったです to きれいではありませんでした or きれいじゃなかったです: a na-adjective was treated as an i-adjective. Record the category before correcting the ending rather than memorizing an isolated replacement.

To say that you did not read yesterday, 昨日、読みません needs 昨日、読みませんでした. But 明日、読みません can describe not reading tomorrow; ません is not automatically wrong. After correcting a pattern, try a new word, such as 寒い instead of 高い or 会社員 instead of 学生, to check transfer.

Use all four types in one original situation

Yesterday Kobayashi did not read this book. At that time, the book was not expensive, the room was not clean, and Kobayashi was not yet a student. Make four polite past-negative statements, then their plain equivalents. Preserve the information while changing style. This is an original conjugation task, not a textbook quotation.