Affect and effect are easy to mix up. They sound similar and both relate to change.

The fastest rule is this:

• affect is usually a verb ("to influence")
• effect is usually a noun ("a result").

In other words:

• If a sentence needs an action (because something causes change) use affect.
• If it needs a noun/thing (the change itself) use effect.

This simple check works in most US English writing.

Exceptions

There are two common exceptions.

First, effect can be a verb meaning "to bring about" or "to make happen," often in formal or technical contexts: to effect a policy change.

Second, affect can be a noun in psychology, referring to a person's emotional expression: flat affect. These are less frequent than the main rule, but knowing them helps you read and write with confidence.

Try this quick test when you hesitate. Replace the word with influence or result. If influence fits, choose affect (verb). If result fits, choose effect (noun).

Example Sentences

• A2: Lack of sleep can affect your mood. (influence - verb)
• A2: The new rule had a big effect on the team. (result - noun)
• B1: Sunlight affects how fast the plants grow. (influence - verb)
• B1: One effect of the storm was a citywide power outage. (result - noun)
• B2: After therapy, his affect was brighter and engaged. (psychology/mood - noun)

FAQs

Q1: How do I decide quickly between affect and effect? A: Ask what the sentence needs. If it needs an action (to influence), use affect (verb). If it names a result, use effect (noun).

Q2: When is effect a verb? A: Use effect as a verb in formal writing to mean "bring about" or "cause to happen," as in to effect change, to effect a merger.

Q3: What about affect as a noun? A: In psychology and mental-health contexts, affect (noun) means a person's observable emotional state or expression, e.g., flat affect, constricted affect.