"Young Goodman Brown" is an excellent story to read to understand the concept of ambiguity, which in this case refers to a richness in meaning resulting from multiple understandings interacting with each other all at once.  An important critic, I. A. Richards, says this about ambiguity in reference to poetry, but it can be applied to fiction as well: " A word ... can equally and simultaneously represent vastly different things.  It can effect extraordinary combinations of feelings.  A word is a point at which many different influences may cross or unite...."  Think about this multiplicity in meaning and effect as you reread "Young Goodman Brown" or any good poem. That story can take place in Brown's head all as a dream, it could have happened in a fantasy sort of way (as a result of guilt) in his subconscious, and then each of the things he sees represent different emotions situations (all at once) as well. The story doesn't mean either this or that but both and many ideas.

This question is the very essence of this story. The reader is never made to be sure if he had dreamed the whole episode, or if he had indeed experienced it. The tragedy truly lies in the note at the end of the tale, in which we learn that he grew suspicious of everyone and lived out his days in a dismal existence because he was never able to trust whether he experienced that night or not.