Inflection
Japanese is very regular when it comes to inflections. There are a few different categories of words that inflect differently from each other, but exceptions to these categories are very few.
Ichidan Verbs
The simplest kind of word to inflect. All of these verbs end in る (but not all verbs that end in る are in this category!) and most of the inflections involve dropping the る and adding something else.see (dictionary)
み
見
る
saw (past)
み
見
た
don't see (negative)
み
見
な
い
want to see (desire)
み
見
た
い
eat (dictionary)
た
食
べ
る
ate (past)
た
食
べ
た
don't eat (negative)
た
食
べ
な
い
want to eat (desire)
た
食
べ
た
い
Godan Verbs
These are more complex as there are five subcategories that each inflect slightly differently. The main idea with godan verbs is that the inflection depends on the last kana of the verb, which is mutated in a way that the consonant often remains the same but the vowel changes.write (dictionary)
か
書
く
wrote (past)
か
書
い
た
don't write (negative)
か
書
か
な
い
want to write (desire)
か
書
き
た
い
learn (dictionary)
まな
学
ぶ
learned (past)
まな
学
ん
だ
don't learn (negative)
まな
学
ば
な
い
want to learn (desire)
まな
学
び
た
い
Adjectives
Also called い-adjectives because they all end in い to differentiate them from な-adjectives which act more like nouns, and as such, don't really inflect. い-adjectives usually inflect by dropping the い and adding something else.cold (dictionary)
さむ
寒
い
was cold (past)
さむ
寒
か
っ
た
not cold (negative)
さむ
寒
く
な
い
fun (dictionary)
たの
楽
し
い
was fun (past)
たの
楽
し
か
っ
た
not fun (negative)
たの
楽
し
く
な
い
A few very common exceptions to these categories include する, 来る, and 行く (this one is mostly regular).