So I'm trying to understand Genki's preferred past negative form of です, that is: じゃなかったです. I'm confused by the なかった.

As I understand it from this source, this is a combination of two 助動詞: the 連用形 form of ない continued with た. However, wiktionary lists the 連用形 form of ない as なく.

なくた sounds a lot like なかった, so it seems reasonable to assume this is a vowel shift to avoid the awkward transition between U to T in KUTA, but, since I'm a beginner, I wanted to make sure - are there other grammatical processes in place that I've missed?

Which leads me to the following overall theory:

There are five "lexemes" in play here

  • じゃ -> DEWA relating the verb phrase to the rest of the sentence
  • なか -> NAI informing of negation
  • った -> TE informing of past
  • です -> DE relating the 助動詞 to ARIMASU -> informing of "existence"

these are combined with somewhat irregular conjugation process which involves shifting verb roots and auxillary verbs into one of a few base forms and then combining them. I assume the grammar of this process is more descriptive than prescriptive, and the speaker typically memorizes a list of common conjugations and common exceptions, rarely applying the rules to create new verb constructs. Or is there a formal grammar to this process described somewhere?

  • 2
    Hi, I was sure I had seen a question about this before and here it is, hopefully this one helps: japanese.stackexchange.com/questions/73025/…
    – OtheJared
    Jan 23 at 6:59
  • 1
    Yep, just as @OtheJared has posted -- that linked thread should answer your questions about ~かった, the past-tense ending for all ~い adjectives. Jan 23 at 9:36

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