In this sentence, which one to use and why:
He is not going to change his practices based on (their)(they're) being unpresidential.
In this sentence, which one to use and why:
He is not going to change his practices based on (their)(they're) being unpresidential.
It is most certainly their
He is not going to change his practices based on their being unpresidential.
Their is the possessive of they and they're is a shorter form of "they are"
The sentence here refer's to the idealogy of a "group" of people and the sentence above cannot permit "they're" in any possible manner as it collapses the core value of the sentence.
Just remember the simple trick - They're is nothing but a shorter way of saying They are.
I'm pretty sure it's their. they're forms a clause, which leads to the need of some leading words like based on that they're ... or based on the fact that they're ....