P & C.

P: How do you spell certainly?
C: C-E-R-T-A-I-N-L-Y.
P: Ok that looks right.
P: But you spell certain c-e-r-t-E-n.
C: Uhhhh. No. Certain and Certainly are the exact same word only one has an L-Y on the end. (in my head: DUH!)
P: Are you positive?
C: Um no. Actually, I'm certain.
P: ha ha. no really, are you positive?
C: Yes. I am certain that certain and certainly are the same word only one is a verb and one is an adverb.
P: Huh?

*just wanted to add that I'm in no way trying to make my husband look stupid, nor do I think he is. This is just an example of a typical conversation between us: two people who never like to be wrong.