Page 161 - Basic Japanese

The negative of adjectives is a phrase consisting of the

plain INFINITIVE + arimasen (or nai desu) ‘does not exist.’

atsuku it’s not hot
arimasen

atsuku nai it’s not hot

desu
it was not hot

atsuku arimasen deshita
atsuku it was not hot

nakatta desu

atsuku it will (probably) not be

nai deshō hot.

This is discussed further in 5.11.

4.2. Plain and polite forms

For the same inflectional category, like imperfect or perfect,

a Japanese verb, adjective, or copula may have two forms: a
plain form and a polite form. In familiar speech, only the
plain forms occur. But in polite speech, the plain forms are

limited in occurrence to some place other than at the end of
the sentence. So, in the polite style of talking, you will say

both of the following sentences:

Ame ga furimashita.

It rained.