The present perfect tense is formed by using the helping (auxiliary) verb “has” or “have” in front of the main verb in the past participle form (ends in “ed” or “en” for regular verbs). This tense is used to show experience, change or a situation that is ongoing. Even if the experience occurred in the past, the tense focuses on if you did something, not when it occurred. Changes or new information can occur in the past or can happen currently. Situations that are ongoing and start in past, continue through the present and possibly into the future are also shown by this tense. “For” and “since” are often used with this tense; “for” refers to a period of time, and “since” refers to a point of time in the past. Consider the following examples:
Example 1: She has tried caviar (the experience was in the past, but she has a memory of it now).
Example 2: She has bought a new computer (shows change – she didn’t have a new computer yesterday, but she has one today).
Example 3: She has lived there since the age of two (situation started in the past, is happening now and is likely to continue in the future).
Example 4: Nancy has been here for 30 minutes.
Example 5: Nancy has been here since 2:30 p.m.