While beginning to learn Chinese, I encounter 叹词 (tàncí) and 感叹词 (gǎntàncí) for the equivalent meaning of interjection in English. I would like to know why the symbol 感 (gǎn) meaning 'to feel' is added and if there is a resulting difference in meaning. In other words, is it proper grammar or necessary to include the 感 symbol?
There is virtually no difference. Perhaps
嘆詞 is more concise than
嘆/叹 itself is seldom used alone in modern Chinese. Modern Chinese tends to use bisyllabic words. So we say
感嘆 (to interject),
讚嘆 (to praise),
嘆息 (to sigh) to 'augment' or 'specify' the meaning of
嘆詞 is already bisyllabic; but it still doesn't hurt to say it as
感 bears the concept of 'to feel'. You interject after you experienced an emotion. It confers neutrality and generality to the word
感嘆 (compare with
讚嘆, which is fairly positive).