갖다 vs 가지다: much like 해 instead of 하?

Question

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 아.

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 아.

And, if a verb root ends in "ㅗ", that vowel contracts with the chaining 아 as "ㅘ": 보다 (po-da) becomes 봐요 (pwa-yo).

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 해요 (statement), 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?

Answer 1

Commenting on what you said, a verb's present tense form is always different from the infinitive form (base form). 알다 is only the base form, and 안다 is the present tense -다 form (ㄹ-irregular conjugation turns ㄹ to ㄴ). Likewise, 가다 becomes 간다, 때리다 때린다, 먹다 먹는다, etc. Only for adjectives the base and the present tense -다 form are the same, as in 크다, 높다, 부끄럽다, 행복하다, etc. which are both base forms and present tense forms.

Also, 해 is a contraction of 하여 which has a connecting 여 instead of 아 or 어 (여 is used like this only for 하다, perhaps because the normal 하아 would make a muddled sound with the two syllables indistinct, or because of some other etymological reasons).

• 하(다) + 여 -> 하여 -> 해. (ex. 하여서 -> 해서, 하여도 -> 해도, 하였지만 -> 했지만)

갖다 is a contraction of 가지다, but the way it is contracted is quite different from the vowel contraction of 해. 가지 in 가지다 is optionally shortened to 갖 (i.e. ㅣ drops and 가 and ㅈ fuses into single syllable), but this is allowed only when the verb ending after 가지 starts with a consonant.

So,

• 갖고/가지고, 갖지만/가지지만, 갖더라도/가지더라도, 갖는/가지는 - all correct.
• 갖어, 갖어서, 갖으면, 갖을 - incorrect. Should be 가져, 가져서, 가지면, 가질 based on the original 가지다.

There are several words with consonant contraction like this, such as 디디다/딛다, 서두르다/서둘다, 머무르다/머물다, etc. Contraction is not allowed if the ending starts with a vowel. because otherwise you would have confusing pairs of conjugation forms, like 디뎌 (디디(다) + -어 -> 디뎌) and 딛어 (딛(다) + -어 -> 딛어: not allowed).