What is the difference between plain form and dictionary form of the verbs?

Question

Can someone explain to me in colloquial term the difference between plain-form（普通形【ふつうけい】） and dictionary-form（辞書形【じしょけい】）of the verbs? As far as I can tell there is no difference between the two but my school book says plain-form and dictionary-form separately.

I would really appreciate it if someone can clear this up for me. Thanks.

Answer 1

My guess is that your book talks of "plain-form" when is referring to a style of speech. For example, in casual conversation you use the plain-form as opposed to the "polite-form" (普通形{ふつうけい} and 丁寧形{ていねいけい} respectively in Japanese).

In some cases this happens to be the same as the dictionary-form or 辞書形｛じしょけい｝. Specifically in the non-past and positive case:

For example:

Polite: 学校に行きます。

Casual: 学校行く。

In the second case you're using a plain-form that happens to be just the dictionary form. So there is no difference here.

However, in general the "plain-form" could be really anything. That is, whatever the conjugation of the verb you still call it "plain form". Using the same example as above:

Polite: 昨日、学校に行きませんでした。

Casual: 昨日、学校行かなかった。

So in this second example, the verb is in the the negative past plain form. So you notice that although this is still called "plain-form" it is not the same as the dictionary form in this case (the latter being 行く of course).

So, to resume:

Dictionary form: is the form of the verb as it is found in the dictionary (not surprisingly).

Plain form: it indicates a form of the verb that is generally used in casual/non-formal conversations and it includes present/past and affirmative/negative conjugations (in other words dictionary/root form, -nai, -ta, and -nakatta forms).

You can see more here.

Answer 2

If you refer to 普通形{ふつうけい} as plain form, you should know that 辞書形{じしょけい} is part of the 普通形{ふつうけい} as the less polite equivalent to the マス形{けい}.