These words are tough for two reasons:
- Each can be a noun or a verb.
- Some of their uses are much more familiar than others.
Let’s break it down:
Affect: the experience of emotional states, or the manifestation of those states
I looked into the killer’s face, but he was stone cold: I couldn’t discern any affect at all.
He didn’t look happy; he had a depressive affect.
Effect: impact, result or outcome
Did Trump’s election have an effect on you?
How did David Bowie’s music affect you?
Affect (secondary definitions): pretend to think or feel something, do something to try to earn admiration
Sergey Kovalev was his next-door neighbor, but he affected indifference.
In his later years, my father affected an aristocratic accent.
Effect: make happen, bring about
I’m running for office because I hope to effect change.*
*In this case, it wouldn’t make sense to say, “I hope to affect change.” You don’t want to influence change. (“Change” is doing fine without your influence.) You want to make change happen.