on Writing Forward:

Homophones can be confusing. Luckily, there’s an easy way to remember affect vs. effect.
I see it all the time: affect and effect mixed up as if they were completely interchangeable.
But they’re not.
These two homophones may sound exactly alike, but they don’t even belong to the same parts of speech!
If you’ve ever written one of these words and scrunched up your eyebrows wondering whether to spell it with an a or an e, then this grammar lesson is for you!