were?

[tilly]

I have a question about the grammatical form of this sentence.

"If they were to leave, I would be happy.

Were is used for past tense, so why is it used in this sentence? WHy do we use were when we're talking about the future?

Thank you-

[Tdol]

Because it isn't true- they are leaving at the moment, nor do they look as if they are going to, so we use the past to show it's imaginary rather than real.