Affect vs. Effect: Which One Do You Need?

Affect is almost always a verb. It means to influence or change something. "The rain affected our plans."

Effect is almost always a noun. It's the result of a change. "The effect of the rain was a canceled picnic."

The exceptions trip people up. "Effect" can be a verb when you mean "to bring about", "The president effected new policy." Rare, but real.

"Affect" as a noun appears in psychology: "The patient showed flat affect." Unless you're writing clinical notes, you probably won't need this.

Quick test: if you can swap in "influence," you want affect. If you can swap in "result," you want effect.