sentences

[plin]

It's them who have to leave, not me.

It's they who have leave, not I.

It's they who have to leave, not me.


Is there a fool-proof way for one not to get mixed up with these kinds of sentences? Many thanks.



Plin.

[Pete]

It's them who have to leave, not me.

It's they who have leave, not I.

It's they who have to leave, not me.


Is there a fool-proof way for one not to get mixed up with these kinds of sentences? Many thanks.



Plin.
There are 2 separate aspects. First, you note that a connecting verb (like "is" connects a subject (nominative case) with a predicate noun (nominative case). Thus the complement, the term after the connecting verb, is a nominative pronoun like "he", "they", etc.

(If you have a transitive verb, the complement is a direct object, in the objective case: "him", "them", etc.)

That sort of analysis should help you pick that pronoun correctly.

For the second part, you have to note that this form is "short" for a longer complete sentence. To see what word is correct, you have to create the full sentence that it is short for.

Look at your second sentence (since that is the correct one). It expands to the following:

- It's they who have to leave; it's not I who have to leave.
Once the sentence is completed that way, the logic for the first clause gives us the answer. Since the verb is "is", the complement is subjective, so we choose "I".

I hope this helps.