After too/to and your/you’re, effect and affect are probably one of the most frequently misunderstood word pairs in common English, especially for all those out there studying for the TOEFL. In spite of this, the difference between them is actually pretty simple: generally speaking, effect is a noun, and affect is a verb.
If you affect something, you influence it. It usually has a neutral connotation, although it can be used negatively.
Thousands of people are affected by tornadoes each spring.
The new law will affect hundreds of business owners.
We use the noun effect to talk about one thing changing or acting on another.
The effect of bad press on tourism to a given location can be devastating.
The Doppler effect describes how movement can make sounds seem higher or lower depending on where they are relative to an observer.
The adjective form, effective, should be familiar to you; synonyms for it include successful and powerful.
Here’s the good news: these words are common, and their definitions aren’t particularly difficult. But here’s the less good news: Affect can also be a noun, and effect can also be a verb. These usages are far less common than the ones mentioned above, so if you want to stop here, you’ll still be fine 90% of the time. But if you’re an overachiever, read on.
In psychology, affect refers to a psychological or emotional state. You may have heard its adjectival counterpart, affective, which simply means “emotional.”
The shopkeeper’s brooding affect contradicted her otherwise polite greeting.
Sam, who preferred dry, objective writing, was repulsed by the author’s affective prose.
Effect as a verb means “to cause.” Fortunately for us, this is probably the least common meaning in this post, used almost exclusively in one particular environment: to effect a change.
Harsh criticism from both parties effected an immediate and noticeable change in the representative’s policies.
The basic rule of thumb: if you’re not effecting a change, it’s better to avoid the verb “effect.” And really, if you’re shooting for the clearest, least obscure prose you can create, you should avoid using effect as a verb altogether. Just be prepared to see it in older texts.
There is one more less common usage of effect, once again as a noun: it can be used to refer to your personal possessions.
When she departed for Europe, she had sold so many of her possessions that all her remaining personal effects fit into a small trunk.
To sum up:
1. Affect is usually a verb meaning to influence or cause a change in something else.
2. Effect is usually a noun that refers to a change.
3. Affect is also a noun that means the same thing as emotion or demeanor.
4. Effect can, rarely, be used as a verb, meaning “to cause.” It’s almost always used to talk about a change. As long as we don’t run into any tricksters like this one, we will only rarely use this definition.