This document compares and contrasts the present perfect tense and past simple tense. It discusses when to use each tense by examining how the past event affects or does not affect the present. The present perfect tense is used when the past event has present consequences, may happen again in the future, or occurred over a period of time. The past simple tense is used when the past event does not affect the present, is unlikely to happen again, or occurred at a specific time in the past. The document also covers the grammatical forms and inversions/negations of both tenses.