Getting effect and affect confused is a common mistake. For two words that only have a one-letter difference between them, they can end up causing a lot of problems. When are you supposed to use effect and when is affect the right choice?

One rule of thumb to keep in mind is that effect is usually a noun, while affect generally acts as a verb. When you’re writing about a result, for example, you should use effect. When you’re writing about influencing something, affect is the word you’re looking for. So a sentence with effect would be something like “The gloomy weather had a negative effect on my mood.” A sentence with affect would be something like “His bad mood didn’t affect me.” However, this noun vs. verb rule of thumb does have exceptions that you should be aware of.

Effect can be used as a verb, although this is usually rare. When it’s used as a verb, it means to bring about or cause something to happen. When affect is used as a noun, it’s used to refer to someone’s outward expressions. This is also rare and mainly appears in psychology texts and other writings. A sentence with effect as a verb would be something like “She will effect these changes in company policy next week.” A sentence with affect as a noun would be something like “He usually had a flat affect in social situations.”

While both of these uses are acceptable, they’re rarely used in everyday writing. Unless you’re writing about someone in a psychological sense, it’s better to use expression or mood to describe emotions or facial expressions. Similarly, unless you’re writing for a business or corporation, you’re better off using a different word than effect as a verb, such as cause or implement.

If you’re still having trouble remembering when to use effect or affect, one trick to try is saying it out loud or in your head. These two words have a slight difference in the way they’re pronounced, which could help you determine which one to use. Effect is usually pronounced with more of a short “I” sound at the beginning, as in the word is, although some people pronounce it with a long “e” sound, as in the word eat. Affect is normally pronounced with more of a short “u” sound at the beginning, as in the word up, rather than a short “I” or long “e.”

How can you remember whether to use effect or affect in a sentence? Your best bet is to use the noun vs. verb rule of thumb. Despite the rare exceptions, effect is almost always used as a noun, while affect is almost always used a verb. Sticking to this rule of thumb should steer you in the right direction when you need to use one, or even both, of these words. For example, “The harmful effects of the drugs affected his well-being.” This sentence puts both of these words to use and does so according to the noun vs. verb rule of thumb. The effects are results that occurred and influenced, or affected, someone’s well-being.