As I was studying clauses, I came upon the following definition:
"a clause is a group of words that contain a subject and a verb"
Coming from a website about grammar, I would automatically consider that to be a correct expression. However, upon diving into the depths of English morphology, I started doubting myself.
In the structure "a group of words", I consider "a group" to be the subject, and "of words" to be an attribute of the subject (what type of group? a group of words). As the subject always concords with the verb and, to me, "a group" is the subject, the correct way of wording the structure I mentioned at first would have to be "a group of words that contains". This is because "a group" is singular, and thus, the verb must be singular as well.
To further dive into the meaning of the structure, "a group of words that contains" suggests that it is the group that contains a subject and a verb, as opposed to the words containing a subject and a verb. If you said "a group of words that contain", you would put "words" in concordance with the verb, suggesting that the individual words are the ones that are supposed to contain a subject and a verb, as opposed to the group of words.
TL;DR: Which one is correct? "A group of words that contains a subject and a verb" or "a group of words that contain a subject and a verb"?