It’s not random! You need to get good at identifying the verb groups. Different resources name the groups differently, but the Ministry of Education (and other stuff) names them 一段(いちだん)、五段(ごだん)、and 不規則(ふきそく) verbs.
一段 verbs never change any part of the core verb. These all end with る in the basic form. They trade out the る at the end for て in te form. Look for words where the ます form has an “e” vowel right before the ます or a single hiragana in front of the ます and you’ll find most of them.
五段 verbs change the spelling of the final hiragana in the core verb. They might be spelled with る as the final hiragana. Look for verbs that have something other than る at the end of the basic form – they’re all in this group. Look for verbs that have at least two hiragana and the last vowel sound before the ます is an “i” sound; they’re in this group too.
In te form, replace endings for 五段 verbs like this:
う、つ、る are replaced with って む、ぬ、ぶ are replaced with んで く replaced with いて ぐ replaced with いで す replaced with して
There are a couple of exceptions, but you’re early enough in your learning that いく becoming いって is probably the only one that will matter for a long time.
2 comments
It’s not random! You need to get good at identifying the verb groups. Different resources name the groups differently, but the Ministry of Education (and other stuff) names them 一段(いちだん)、五段(ごだん)、and 不規則(ふきそく) verbs.
一段 verbs never change any part of the core verb. These all end with る in the basic form. They trade out the る at the end for て in te form. Look for words where the ます form has an “e” vowel right before the ます or a single hiragana in front of the ます and you’ll find most of them.
五段 verbs change the spelling of the final hiragana in the core verb. They might be spelled with る as the final hiragana. Look for verbs that have something other than る at the end of the basic form – they’re all in this group. Look for verbs that have at least two hiragana and the last vowel sound before the ます is an “i” sound; they’re in this group too.
In te form, replace endings for 五段 verbs like this:
う、つ、る are replaced with って
む、ぬ、ぶ are replaced with んで
く replaced with いて
ぐ replaced with いで
す replaced with して
There are a couple of exceptions, but you’re early enough in your learning that いく becoming いって is probably the only one that will matter for a long time.
u/iammrnoone answered your question in his post [Brief Japanese – history of て form, why is it so iregullar…](https://www.reddit.com/r/LearnJapanese/comments/v08pbp/brief_japanese_history_of_%E3%81%A6_form_why_is_it_so/)