You use then to introduce the second part of a sentence which begins with 'if'.
The first part of the sentence describes a possible situation, and then introduces the result of the situation.
The meaning of then is at that time.
How to use then in a sentence.
At that time at the time mentioned;
Used to indicate what happened or happens next
Definition of then adverb from the oxford advanced learner's dictionary.
Used to refer to a particular time in the past or future.
Life was harder then because neither of us had a job.
He's always harking back to his childhood and saying how things were better then.
Just then, the lights went out.
The train leaves at three minutes to eight, so we'd better get there a few.
From longman dictionary of contemporary english then1 /ðen/ s1 w1 adverb 1 at a particular time in the past or future i wish i had known then what i know now.
It was then that i realised.
Then is a very common word that's used in situations involving what comes next—either in terms of time (as in just then, the door opened or we saw a movie and then we drove home) or a.