How does one handle the interjection in terms of sentence structure. If I use an interjection of one word, is this a proper use of English. Does it count as a grammatical sentence? Is it a fragment? Must it always be followed by a comma and linked to a sentence to be grammatically correct. For example, in the sentence, he loved the wilderness. If I want to follow it with a Yes! for emphasis, does the Yes! standing alone create a fragment or sentence. Is it grammatically?