I'm a post-beginner in Korean. Before I go to the point, I guess I should summarize what I know about Korean grammar likely related to this question.
I know that, in Korean, the radical of the verbs (the root without the
다 ending) sometimes needs a "concatenation" suffix so that it can be linked to other "functional" suffixes.
The "chaining" suffix is required to form the
요 statements. I know that the "friendly" way of telling I eat is
먹어요 (meog-eo-yo) and not 먹다. Likewise, I know will be
알아요 (al-a-yo) and not just 알다 (which is both an infinitive and a plain present form, but inappropriate in most conversational contexts).
So far so good. The concatenation suffix is
어 when the last vowel of the verb root is NOT "ㅏ" or "ㅗ". Otherwise, the concatenation suffix is
These suffixes, however, may undergo contractions sometimes: two vowels "a" in a row are blended into a single one, as in
사요 (sa[-a-]yo). If a root ends in "ㅣ", that vowel blends with the chaining 어 as "ㅕ":
기다리 + 어 + 요 = 기다려요 (kidaryeo-yo).
Talking about contractions, if a root ends in "ㅡ", the concatenation suffix will depend on whether "ㅡ" is the only vowel or not (of the radical).
쓰다 (sseu-da) becomes
써요 (seo-yo), because "ㅡ" is assimilated by the required
어, provided it's the only vowel of the verb. But if the radical has two syllables, the concatenation suffix will be determined by the vowel which preceded "ㅡ":
기쁘다 (gippeu-da) becomes
기뻐요 (gippeo-yo) because the vowel "ㅣ" requires the
어 suffix, but
모르다 (moreu-da) becomes
몰라요 (molla-yo) because "ㅗ" takes the chaining suffix
And, if a verb root ends in "ㅗ", that vowel contracts with the chaining
아 as "ㅘ":
보다 (po-da) becomes
The only exception to the aforementioned rules seems to be the verb
하다, which, instead of being followed by a concatenation suffix, is replaced by a "concatenation radical",
해, used in expressions such as
했어요 (past tense),
해주세요 (request), etc.
After this long recap, then to the gist of my question: is
갖다 a contracted variant of
가지다 used in concatenations, I mean, is
갖 a transformed version of
가지다 as much as 해 is a transformed version of 하다?