In my text messages/kakaotalk conversations I recently happened to need these expressions and while I understood them correctly, there was just this nagging feeling that I didn’t understand the exact difference between them. Today I asked my language partner about the specific differences:
그치 / 그쵸 vs. 그렇지/ 그렇죠
그치 is a shorter version of 그렇지. Due to losing the middle syllable, ㅊ is used instead of ㅈ to make the sound stronger to compensate for the ㅎ that is left out.
그치/그쵸 is mostly used in spoken language, but not often in writing because it looks a tad more awkward than 그렇지 when written down. Both can be used both as a question (“right?” and as an answer (the affirmative “right”).
그치/ 그쵸 is slightly less formal than 그렇지 / 그렇죠.
Used as an affirmative response. Roughly translates into “I see”.