The English language is populated with so many confusingly similar word pairs that even professional writers slip up sometimes. One of the most notorious examples is affect and effect—and not just because their spellings only differ by a single letter. Their definitions are related, too.
According to Merriam-Webster, affect means “to produce an effect upon.” Effect is, well, that effect (or, in clearer terms, “a change that results when something is done or happens”). In short, affect is most commonly used as a verb, and effect is frequently a noun. Claudine James, a middle school English teacher known as @iamthatenglishteacher on TikTok, has a handy mnemonic device to help you remember this.
Think of the a in affect as standing for action. If you’re describing an action, you should probably choose affect. For example: The strike affected my bowling score even more than I had expected. The t in effect, on the other hand, can stand for the. If the word is preceded by an article—a, an, or the—or any other adjective, it should probably be effect. For example: The strike had a positive effect on my bowling score.
All that said, there are certain situations in which affect can be used as a noun and effect functions as a verb. If you’re describing someone’s emotional reaction conveyed through facial expression, tone of voice, body language, and/or other visible indicators, the word you want is affect (pronounced with the emphasis on the first syllable). For example: Based on her affect when I told her I’d gotten the job, I knew she was excited for me.
The verb effect means, according to Merriam-Webster, “to cause to come into being,” “to accomplish,” or “to put into operation.” Though these definitions do admittedly sound similar to affect as a verb, they’re not exactly the same. Affect involves causing change to something that already exists, while effect is about causing something to happen in the first place. If you effect a plan, you’re carrying out a plan. If you affect a plan, you’re changing a plan that already exists. If you effect change, you’re causing change to occur. If you affect change, you’re influencing change that is already occurring.