The Origin of のだ


I've recently been trying to fit the explanation particle のだ in with the logic
of Japanese and I was wondering if it had its roots in another Japanese word
or something of the sort. Particularly, it seems as if it might be an
abbreviation of ものだ, being that these two constructions can have similar use.
They both seem to add a layer of relevance to a statement by saying it is a
thing, in the "it is the case that" sense. Follow that, might the の used to
normalize verbs also be of this origin? And if at all possible is any of this
related to the possessive の?




だ is an auxiliary meaning "be"，a suffix for 體言（words do not have
conjugations，like nouns), かめらだ means " _Is_ camera"

In のだ, の is not possessive, but "formal subject", a high-level abstract noun.
It doesn't have real meanings, **there it is because the sentence needs a noun
from a grammar view.**

e.g. 行く, you wanna add だ to emphasizing, 行くだ，but だ is for nouns, so you have
to add an abstract noun, 行く **の** だ.

です is the polite version of だ，so there is のです. so 行きます => 行くのです

Why do we wanna add のだ/のです? For emphasizing and explanation.

BTW, if you add のだ・のです to na-adjectives, you need な，なのだ・なのです，that is how na-
adjectives modify nouns. e.g. 好きなのだ．

In speaking language:

の can be ん，so 食べたのです=食べたんです

だ・です can be omitted, so it becomes "行くの", 好きなの

and だ・です can also be replaced by か，so 食べないのか, this is usually used by males.

