How to say "I think" in Japanese

A) Example with Noun + Copula:

For example, 明日は休みです (ashita wa yasumi desu) means “tomorrow is a holiday.”

To turn this into an “I think” statement, first change the copula です (desu) to plain form だ (da)

The plain form of the sentence is 明日は休みだ (ashita wa yasumi da)

The second step is to add 〜と思います (~to omoimasu) to the end of the sentence.

B) な-adjectives (na-adjectives):

Both nouns and na-adjectives use だ (da) before 〜と思います (to omoimasu).

Let’s see an example with the na-adjective 親切な (shinsetsu na) which means kind.

先生はとても親切です (sensei wa totemo shinsetsu desu) means “My teacher is very kind.”

To change to an “I think” statement, first change です (desu) to だ (da)

Then, add 〜と思います (~to omoimasu) to the end of the sentence.

The result is an “I think” statement: 先生はとても親切だと思います (Sensei wa totemo shinsetsu da to omoimasu) – I think my teacher is very kind.

C) い-adjectives (i-adjectives) and verbs:

For i-adjectives and verbs, DO NOT put だ (da) before 〜と思います (to omoimasu)

猫は可愛いです (neko wa kawaii desu) means “Cats are cute.”

To make the plain form of an i-adjective, just take off です (desu)

To make it an “I think” statement, just add 〜と思います (~to omoimasu) to the end of the sentence.

The result is an “I think” statement: 猫は可愛いと思います (Neko wa kawaii to omoimasu) – I think cats are cute.