past-n; 3 Senses

Sense Number 1: pertaining to general time

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

Sense Number 2: pertaining to one person's life

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

Sense Number 3: past tense

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