How to convert verbs from polite form to dictionary form?


Does anyone have a good rule for converting to dictionary (u)form from masu
form regarding the different verb groups? Most websites start with dictionary
and go to masu but I learned starting with masu.




As you may know, Japanese verbs are either godan (five step) or ichidan (one
step) verbs.

Godan Verbs:

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             remove the masu e.g. ikimasu -> iki
             then change the final syllable to a 'u' sound, e.g. iki -> iku
             other examples: iimasu -> ii -> iu
                             nomimasu -> nomi -> nomu
    
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Ichidan verbs:

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               remove the masu
               then add 'ru', e.g. tabemasu -> tabe -> taberu
    
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The trick of course is knowing what sort of verb is it. Generally, verbs whose
final stem syllable (before masu) is an 'e' sound are ichidan (tabemasu,
akemasu). Howeverm, there others (dekimasu, karimasu). So, you will have to
learn it for each verb. However, it's quite easy to form the dictionary form.




As James said, without knowing the group of the verb, you can't really guess.
Note that this is also true for the inverse step : i.e. you cannot, simply
from the dictionary form guess what is the ます-form nor the て-form.

From there, look for go-dan (`五段`) or ichi-dan (`一段`) in your dictionary.
During my studies, my teacher also reffered to them as "strong" and "weak"
verbs respectively.

Then, it is pretty simple :

  * For godan:

    * Remove the ます stem
    * Take the last syllable of your verb, before the ます stem.
    * Change it to the "u" sound of the same line. (Be careful, the "u" sound of the "t" line is `つ` and not `テゥ` !).
  * For ichidan:

    * Remove the `ます` stem
    * Add `る`

So now, the real question is, in which category does your verb fall in ?

  * If the last syllabe of the dictionary form (a.k.a. the one just before your ます stem) is a "e" syllabe, it is ichidan. See for example, 食｛た｝べる, 教{おし}える, 負｛ま｝ける...
  * If your verb has only one syllabe (excluding the ます stem) it is also ichidan ! For example 見｛み｝る/見ます、着{き}る/着ます. Be careful, some of this verbs have false friends : they have the same dictionary form but are actually godan. Check for example 着る and 切{き}る/切ります.
  * If your verb ends with an `i` vowel, it is most often a godan, see 飲｛の｝む/飲みます, 書｛か｝く/書きます, 勝{か}つ/勝ちます. However, you really need to memorize the exceptions to this rule : some are ichidan, like 起｛お｝きる/起きます, 降｛お｝りる/降ります, 借｛か｝りる/借ります
  * There are a few exceptions to this rule, most notably :

    * する/します
    * 来｛く｝る/来｛き｝ます

As a side note, when you will know about more forms, you can always deduce the
group of a verb from two forms, and from there construct the other ones. godan
verbs change at all forms (five, hence godan) and add a suffix while ichidan
never change their root and are simply added a suffix (hence a one step verb).

Good luck in your studies !

