A simple Google search reveals that the word
that can be used in many ways: as a pronoun, determiner, adverb and conjunction. I'm wondering about its usage specifically as a conjunction.
Take the following two examples:
I think that I know who sings this song
I think I know who sings this song
From a colloquial standpoint, I would use the shorter version (the latter).
However, what is the grammatically-correct form? Is the word
that, when used as a conjunction, necessary from a grammatical standpoint? It seems superfluous to me.