@sanjanag I’ll try to break this down by consonant group so hopefully the pattern is more explicit. I’ll be using some rōmaji because these patterns are easier (for English speakers) to see when the stem vowel can be separated from the consonant. Honestly though, I’d be surprised if most beginners’ textbooks don’t have some version of this table somewhere for the 〜た forms of godan verbs. Mine did. Then again, that was a weekly summary lesson that was meant to teach conjugation. Maybe other beginners’ textbooks don’t aim to get students conjugating independently fast… Also, the rule is the same for both the 〜て and 〜た forms of verbs, so be sure to use this knowledge to its fullest potential.
If I’m not wrong, the way the conjugations worked historically was that the い form of the verb (aka the masu-stem that we see in front of ‘masu’ all the time) would have て or た attached to it. Over time, pronunciation changes occurred, and we ended up with what we have now.
Irregular verbs
I’ll just get these out of the way since they’re both fairly important and fairly rare (as a proportion of all verbs, regardless of frequency). There are only three main ones: する、来る and 行く. You could add だ・である・です to this list, but that’s really just a special application of ある. There are a few other verbs that are irregular but only in the 〜て・た forms, like 問う, but you can just learn those as exceptions to the rules when you come across them. In any case, learn the conjugation patterns for these three as well as you can through whatever means necessary. To help yourself, you can probably look for similarities between these verbs and godan or ichidan patterns, like how a stem ending in い seems to do most of the work for all three, but they’re still irregular overall.
Ichidan verbs
These are the words with only one stem, to which you attach whatever you’re supposed to attach (ます、た、て、other verb to form a compound verb etc). One of the most common examples is 食べる.
Godan verbs
They’re called ‘godan’ (五段) because they have five stems: negation (-A), infinitive/masu (-I), end-of-sentence/noun-modifying (-U), command/imperative (-E), volitional (-O). You can find out what each of these stems is for on Wikipedia or Wikiversity, but if that doesn’t interest you right now, or it seems too technical, don’t worry about it: you’ll come across these forms as you study.
As far as the 〜て・た forms go, there are three broad categories. (You can skip all my explanations and just read the headings in bold, if you prefer):
The endings that become little っ – つ・る・う: historically, they would have been ちて、りて and ひて (most modern -う verbs used to end in -ふ). I’m not sure how you’ll remember this group… You could say
- うつる is a verb that is in this group (I leave you to pick exactly which うつる you want, because there are at least two)
- つる means ‘crane’. Maybe you can lengthen the last syllable for fun in your head (つるー), or go, ‘Ooooh (う), tsuru!’ (‘Ooooh, a crane!’) and imagine the little っ is the crane’s foot or crest.
- Big つ becomes little っ. Logical. R is a sound that often gets reduced in Japanese, so it’s not strange that, say, 売りて became 売って (‘selling’/‘sell and…’). For the I vowel alone… try saying いひて(言ひて)really fast. Don’t you feel like it would be easier without that breathy ひ in the middle? Plus, you can barely hear it, right? Why shouldn’t it become っ?
The endings that become いて・いで – く・ぐ: same test as before – try saying words like かきて(書きて)and およぎて(泳ぎて)really fast. Blocking the airstream in your throat to make the K or G sounds is too troublesome after a while, isn’t it? You might then ask, ‘But why is one て and the other で?’ Well, G is a voiced consonant (the vocal cords vibrate when it’s pronounced), and it’s the voiced version of K, which is voiceless (the vocal cords don’t vibrate). Similarly, T and D are a voiceless-voiced pair. The vocal cord vibrations just got ‘transferred’ to the next consonant.
The endings that become んで – ぬ・む・ぶ: This set is easy. ん is the sound in Japanese that often comes before all sorts of sounds that require you to close your mouth or at least bring your lips really close together. ぬ and ん sound very similar, so that’s no problem. M and B are the two sounds (along with P) for which you must close your lips, otherwise they’re impossible to pronounce. Your mouth ends up in a similar position to what you need to pronounce any of a number of possible sounds for ん, so once again, it’s really natural. As for why it’s で and not て… this is my best guess, but notice how all the consonants involved here are voiced. It would be hard to keep て sounding purely voiceless when you pronounce it after one of these sounds, no?
That’s about it. I figured some explanation might help make these sound changes seem more ‘reasonable’ and thus easier to learn, but I know these explanations might not work for you, and in any case, you’ll need to find a way to make this knowledge your own. All the best, anyhow. 