Which forms of a verb do I need to memorize to distinguish ichidan from godan?


Can I get away with memorizing only these two forms of a verb?

  1. Dictionary form `かえる` ("to return")
  2. Positive polite non-past form, like `かえります`

If I compare these two forms, I can determine whether it's a Type 1
([五]{ご}[段]{だん}) verb or a Type 2 ([一]{いち}[段]{だん}) verb. I can do this by
checking if (for example) `る` gets taken off when I add `ます`, or if it gets
changed to `り`. Does this make sense?

I'm asking because this packet I got tells me to remember the dictionary and
**_past_** forms, but I don't see how this is helpful.

In short, is my method of learning these verbs' types consistent? Thank you in
advance :)




  1. All Type 2 (一段) verbs end in -iru and -eru.   
The **converse is not true** i.e. verbs that end in -iru and -eru may also be
Type 1 (五段).

  2. The conjugation for polite form for Type 2 (一段) is quite straightforward.

    * Remove る, append ます
    * 食べる→食べます
    * 見る→見ます
    * 変{か}える→変えます
  3. The conjugation for polite form for Type 1 (五段):

    * Change final sound to the corresponding one that ends in -i, then append ます
    * 歩く→歩き→歩きます
    * 会う→会い→会います
    * 帰{かえ}る→帰り→帰ります

I think the confusion is when the polite form is taken to be the starting
point, and it gets "reverse conjugated" to obtain the dictionary form. In my
opinion, it is much more systematic to start from the dictionary form.

変える and 帰る are both かえる. I suppose your method of "remove ます + る" test for 一段
works sufficiently well.

* * *

> I'm asking because this packet I got tells me to remember the dictionary and
> past forms, but I don't see how this is helpful.

It is "helpful" because the past form is not built from the polite form, but
from the dictionary form. You need to know the dictionary form in order to
conjugate to the past form. Your course probably taught you the polite form
first, so now the thought process you are going to use is probably:

  * polite form→dictionary form→past form

When it is actually:

  * dictionary form→polite form
  * dictionary form→past form

