Affect vs Effect: which is correct?

The one rule that covers most cases

In the overwhelming majority of sentences, affect is a verb and effect is a noun. Affect means to influence or to make a difference to something: rain affects my mood, the news affected the markets, lack of sleep affects your concentration. Effect means a result or a consequence: the rain had an effect on my mood, the news produced an effect on the markets, sleep deprivation has an effect on concentration. The two words describe the same relationship from opposite ends, which is why they feel interchangeable but are not.

The fastest test is the article test. If you can sensibly put the, an, or a in front of the word, you almost certainly want effect, because only the noun takes an article. You would never say the affect on my mood, but the effect on my mood is natural. Conversely, if the word is doing the action in the sentence, sitting where a verb belongs, it is affect.

The exceptions worth knowing

English would not be English without exceptions, and there are two that matter here. First, effect can be a verb, but only in the formal phrase to effect change or to effect something, meaning to bring it about. A manager might effect a reorganisation. This is rare in everyday writing, so if you are not deliberately reaching for that formal meaning, the verb you want is still affect.

Second, affect can be a noun, but almost only in psychology, where affect (stressed on the first syllable, AFF-ect) means an observable display of emotion. A clinician might note that a patient had a flat affect. Unless you are writing about mental health in a clinical register, you will not need this one. Set those two specialist cases aside and the simple rule holds: affect the verb, effect the noun.

There is also the everyday word affected used as an adjective, meaning artificial or pretentious, as in an affected accent. That comes from the verb affect and does not change the core rule; it is just a reminder that affect is the form tied to the idea of acting on or putting on something.

Worked examples both ways

Start with affect as a verb. The strike will affect deliveries this week. Stress can affect your sleep. How did the feedback affect the team? In each, the word is an action being done to something, and you could swap in a synonym like influence without breaking the sentence: the strike will influence deliveries, stress can influence your sleep. That swap test is a reliable backup to the article test.

Now effect as a noun. The strike had a serious effect on deliveries. The drug's side effects were mild. The lighting created a dramatic effect. Each time, the word names a thing, a result you could point to, and it often follows an article or an adjective: a serious effect, the side effects, a dramatic effect. If a synonym like result or outcome fits, you want effect.

Put them in one sentence to feel the difference: the policy affected morale, and that effect lasted for months. The action (affected) and the result (effect) sit side by side, and once you can see them as cause and consequence, the spelling follows naturally.

Why the mix-up happens and how to lock it in

The confusion is built into the words. They are near-homophones in casual speech, both come from the same Latin root facere (to do or make), and both relate to the idea of one thing acting on another. Your ear cannot tell them apart, so the choice falls entirely on the grammar, which is precisely the situation spell-check struggles with: both spellings are real words, so a checker rarely flags the wrong one in context.

A memory hook many writers use is RAVEN: Remember, Affect Verb, Effect Noun. Another is that affect and action both start with a, while effect and end (a result is an end point) both relate to outcomes. Pick whichever sticks. Then, when you proofread, run the article test on every affect or effect you wrote: try to put the in front of it, and if that reads correctly, the word should be effect. That single pass catches almost every error.

Use the quiz above to test yourself on the boundary cases, and paste any draft into a grammar checker as a backstop, but treat the rule as your primary defence, because in the one-in-ten case where the checker is unsure, knowing affect-verb, effect-noun is what saves you.