Japanese "Negative Base", so-called because most of the endings used with Base 1 have a negative aspect.

Godan verbs in Base 1 all end in -a. Ichidan verbs have no Base 1, you just use the stem directly.

To form Base 1 for Godan verbs, follow the pattern with these example verbs, which should cover all the possible phonologies:

The irregular verbs kuru and suru use ko- and shi-, respectively.

Some example endings for Base 1:

-nai Informal present negative. This can be made more polite by adding desu, with no change in meaning.

Furansu-go ga hanasanai.
I don't speak French.

Ototo wa kan-shoku ga tabenai desu.
My little brother doesn't eat Korean food.

-nakute Does not do and ...; without doing; not doing. Mild cause-effect concept.

O-tomodachi ga konakute, doo shimasu ka.
What will you do if your friend doesn't come?
(Literally: Your friend does not come, and what do you do?)

Exceptionally (but predictably), aru becomes simply nakute.

O-kane ga nakute, kaimasen deshita.
Having no money, I didn't buy it.

-nakatta Informal negative past. Very commonly heard in anime, and in speech in general. Again, adding desu raises the politeness level slightly.

I didn't know.

Watashi no tomodachi wa kinoo konakatta.
My friend didn't come yesterday.