"It's actually pretty straightforward. The majority of the time you use affect with an a as a verb and effect with an e as a noun.
When Should You Use Affect?
Affect with an a means "to influence," as in, "The arrows affected Ardvark," or "The rain affected Amy's hairdo." Affect can also mean, roughly, "to act in a way that you don't feel," as in, "She affected an air of superiority."
When Should You Use Effect?
Effect with an e has a lot of subtle meanings as a noun, but to me the meaning "a result" seems to be at the core of all the definitions. For example, you can say, "The effect was eye-popping," or "The sound effects were amazing," or "The rain had no effect on Amy's hairdo."
Common Uses of Affect and Effect
Most of the time affect with an a is a verb and effect with an e is a noun.
So most of the time affect with an a is a verb and effect with an e is a noun. There are rare instances where the roles are switched, and I'll get to those later, but for now let's focus on the common meanings. This is "Quick and Dirty" grammar, and my impression from your questions is that most people have trouble remembering the basic rules of when to use these words, so if you stick with those, you'll be right 95% of the time."
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