Japanese verb base, sometimes known as the "conditional base", because of the few
endings that require this base, most of them have some
conditional aspect.
To form a Godan verb into Base 4, use the following pattern:
For
Ichidan verbs, change the final
u to
e:
Suru becomes
sure- in Base 4.
Kuru becomes
kure- or
kore-, depending on the final ending.
A verb in Base 4 with no ending expresses an abrupt command, as in the familiar
Hanase!
Let go!
Tasukete!
Help!
from anime (see? I bet you didn't realize that at the end of the first episode of Princess Rouge, that guy is shouting out a Godan verb in Base 4 no-ending, did you?). In this form, kuru becomes kore, and suru becomes seyo in two-part verbs and is replaced by yaru otherwise.
Two other endings requiring base 4 are -ba (If/When (I) do), and -ba yokatta (it would be better if (I) had done). In both of these forms, kuru becomes kureba and desu becomes naraba.
Kyoo wa watashi ga hayai kaereba, tenisu o shimashoo ka.
If I return early today, shall we play tennis?
Hayaku tabereba yokatta desu.
It would be better if I had eaten early.
I wish I had eaten earlier.
Base 4 + -ru is the Potential Form of Godan verbs. This ending actually creates a new Ichidan verb, which should be further inflected if necessary.
Hanasemasu ka.
Can you speak?