Why is 帰る conjugated 帰りたい and not 帰たい when adding たい to it?
Is it conjugated this way because 帰る is a godan verb?
As surmised in your question, and confirmed by user3856370 in the comment, 帰【かえ】る ("to return", intransitive") is a 五段【ごだん】 verb, and this is why たい needs that り before it.
The grammar
More specifically, the ～たい desiderative ("want to") ending attaches to the 連用形【れんようけい】, the continuative or stem form of the verb. This is sometimes called the "-masu stem" in English, since it's the form of the core verb that gets the -masu on the end.
Mechanics for 五段【ごだん】 or "type I" verbs
For instance, 行【い】く ("to go") in the plain or dictionary form becomes 行【い】きます in the polite or -masu form. The verb stem here, the 連用形【れんようけい】 for this verb, is 行【い】き. So to conjugate into the desiderative, we would take that stem 行【い】き and stick the ～たい auxiliary or suffix onto the end, giving us 行【い】きたい.
Mechanics for 一段【いちだん】 or "type II" verbs
For the 一段【いちだん】 verbs, the verb stem is the same for all of the different conjugations -- that's actually what 一段【いちだん】 means here, there's just the one 段【だん】 ("grade, step") -- that is, there's just the one vowel on the end, either -e or -i depending on the verb. So for 変【か】える ("to change", transitive), the plain form 変【か】える becomes -masu form 変【か】えます, so we know the -masu stem or 連用形【れんようけい】 is 変【か】え. To conjugate into the desiderative, we take that stem 変【か】え and stick the ～たい auxiliary or suffix onto the end, giving us 変【か】えたい.
Note about homophones
Some verbs, like 帰【かえ】る and 変【か】える, sound almost the same. (The pitch accent is different, but in terms of kana spellings, they are identical.) In these cases, you basically just have to learn which is which and remember the conjugation rules. Thankfully there aren't that many verbs like this. :)
Please comment if the above does not answer your question.
answered Jan 21 '20 at 17:26
