Commentary: past times, yesteryear, yore - the time that has elapsed
Forget the past...
In the past people had to either hunt or gather in order to eat.
WordNet 2.0 Sense Numbers: 1
Commentary: an earlier period in someone's life (especially one that they have reason to keep secret)
Reporters dug into the candidate's past.
His past is littered with dirty little secrets.
WordNet 2.0 Sense Numbers: 2
Commentary: a verb tense that expresses actions or states in the past
The first sentence is the past tense so the next shouldn't be in the present.
Because Fido doesn't differentiate between past and present tense, he gets his leash when George says "walk" or "walked".
WordNet 2.0 Sense Numbers: 3