How “even though” and “even if” differ in sense

Let’s take up today the difference between the contrastive conjunctions “even though” and “even if,” which I know that not a few writers — even professional ones — tend to use interchangeably.

I’d like to emphasize at the very outset that as a rule, “even though” and “even if” are not interchangeable. They are vastly different. “Even though” is for expressing a fact or something that’s real or true, while “even if” is for expressing a supposition or for something imagined or unreal.