The present perfect tense of "not left" is has not left or have not left.
The present perfect tense is used to describe an action that started in the past and continues in the present or has an effect in the present.
Here are some examples:
- He has not left the house all day. (He is still at home.)
- They have not left for their vacation yet. (They are still planning to go.)
- We have not left the office since lunch. (We are still working.)
In these examples, the action of "leaving" started in the past (earlier today, yesterday, or at lunch), but it is still relevant to the present.
The choice between "has" and "have" depends on the subject of the sentence. "Has" is used with singular subjects (he, she, it), while "have" is used with plural subjects (we, you, they) or with the pronoun "I".
