Godan verbs

The 820 godan verbs on the JLPT lists, grouped by the kana they end in. A godan verb moves its final kana along that kana's vowel row: か before ない (書かない), き before ます (書きます), け for the potential and ば forms (書ける, 書けば), こ for the volitional (書こう). Its て and た forms are 書いて and 書いた. Which kana that is decides the て form, and there are four groups: く/ぐ → いて/いで, う/つ/る → って, む/ぶ/ぬ → んで, す → して.