Just had a conversation with someone which morphed into a discussion of grammar and the parts of speech. She wondered, "What part of speech is a word such as 'maybe' or 'probably'?" I answered, "Adverb.........I think." So I went to a website for a refresher on parts of speech and discovered a couple of things.

"Maybe" and "Probably" are adverbs. So I was right. "Therefore" (are you ready?) is an adverb that functions as a conjunction. After skimming through the various parts of speech (compound verbs, prepositions, superlative adverbs, etc.) I realized that I have truly forgotten more than I ever knew in the first place.