In the casual style of speech used with immediate family and close friends and associates, the main verb of the sentence is a plain form rather than a polite form. However, even in a polite sentence, verbs other than the main verb often need to be plain forms, so these must be learned.

Plain present/future form

The plain form of the present tense is the dictionary form. (It is also used for future tense.)

Plain negative and negative past forms

The plain negative ending is -nai, and the plain negative past ending is -nakatta.

For an ichidan (ru-dropping) verb, these endings are added to the stem (the part of the verb obtained by dropping the syllable “ru”). Example: miru -> mi + nai = minai, mi + nakatta = minakatta.

For a godan (u-dropping) verb, these endings are added to the stem ending in the vowel sound “a” (see Verbs). Examples: iku -> ika + nai = ikanai, ika + nakatta = ikanakatta; kau (to buy) -> kawa + nai = kawanai, kawa + nakatta = kawanakatta. (For a godan verb with last syllable “u”, -u -> -wa instead of -a when forming the stem.)

The plain negatives of kuru and suru are konai and shinai, respectively. The plain negative of aru is simply nai. (For comparison, the corresponding polite forms are kimasen, shimasen and arimasen.) Similarly, the plain negative past forms of these verbs are konakatta, shinakatta, and nakatta.

ときどき映画を見る。
Tokidoki eiga o miru.
I sometimes watch movies.

たかはしさんは魚を食べない。
Takahashi san wa sakana o tabenai.
Ms. Takahashi doesn’t eat fish.

お金がなかった。
Okane ga nakatta.
I didn’t have any money; there was no money.

The plain past form

To form the plain past tense for an ichidan verb, add  -ta to the stem. Example: miru -> mi + ta = mita.

For godan verbs use the appropriate change in the following list, depending on the last syllable of the dictionary form of the verb:

su => shita	話す	hanasu	話した	hanashita talked
ku => ita	聞く	kiku	聞いた	kiita asked
gu => ida	泳ぐ	oyogu	泳いだ	oyoida swam
ru => tta	塗る	nuru	塗った	nutta painted
tsu => tta	持つ	motsu	持った	motta held
u => tta	思う	omou	思った	omotta thought
bu => nda	飛ぶ	tobu	飛んだ	tonda flew
mu => nda	飲む	nomu	飲んだ	nonda drank
nu => nda	死ぬ	shinu	死んだ	shinda died

Irregular past tenses

The plain past tenses of kuru and suru are kita and shita, respectively. The plain past tense of iku (to go) is irregular: it is itta (not iita, as the rule would suggest).

As long as the verb at the end of a sentence is in the polite form, any verbs in the middle can be in the plain form without affecting the overall politeness level. This means that the plain form can be used when sentences are joined with kedo, for example, or when they finish with deshou.

体育の先生はいい人だけど、ちょっと変ですね。
Taiiku no sensei wa ii hito da kedo, chotto hen desu ne.
The physical education teacher is nice, but he’s a bit strange, isn’t he!

たかはしさんは英語がわかるでしょうか。
Takahashi san wa eigo ga wakaru deshou ka.
I wonder if Ms. Takahashi understands English?

兄は行かないけど、私は行きます。
Ani wa ikanai kedo, watashi wa ikimasu.
My older brother is not coming, but I am.

今日は金曜日だと思ったけど、違いますね。
Kyou wa kinyoubi da to omotta kedo, chigaimasu ne.
I thought it was Friday today, but it isn’t, is it!

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This page is adapted from “Some Notes on Japanese Grammar,” published for your personal use with the kind permission of Keith Smillie (http://www.cs.ualberta.ca/~smillie/)

Related posts:

1. Polite Japanese Verbs
2. Japanese Verbs
3. Past tense
4. Japanese Grammar – Verbs, Particles, and Sentence Structure
5. Expressing ‘to be’ in Japanese