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 :)
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2012-11-21T02:38:25.493
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2012-11-21T04:56:49.233
2012-11-21T03:16:31.740
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question
verbs conjugations
Which forms of a verb do I need to memorize to distinguish ichidan from godan?
Your method of memorizing plain and polite present forms in order distinguish
between ichidan and godan verbs should suffice. Although keep in mind that it
is only ambiguous when a verb ends in -eru or -iru, so it is unnecessary to
memorize both forms for all verbs. Also worth noting is that godan verbs
ending in -える or -いる are rare. Most of the time these verbs are ichidan.
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2012-11-21T03:51:25.067
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answer
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
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2012-11-21T03:54:34.397
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answer
Yes, you can get away with only memorizing plain and polite non-past as you
suggest.

However, memorizing just the plain non-past and past would work as well, since
if the past form is just created by removing る from the non-past and adding た,
then it is ichidan, otherwise it is godan. This approach might have the
advantage that it relieves you of memorizing the different consonant patterns
in godan, -mu->-nda, -ku->-ita, -gu->-ida etc, separately. But then again, you
probably _should_ memorize those anyway.
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answer