Which sentence uses 'affect' or 'effect' correctly?
- The new lighting will affect how the room feels.
- The new lighting will effect how the room feels.
- The affect of the new lighting was obvious to everyone.
- Scientists studied the affect the medicine had on patients.
Why A? And why not the others?
Correct answer: A. The new lighting will affect how the room feels.
In everyday use, 'affect' is almost always the verb, meaning 'to influence' or 'to change', while 'effect' is almost always the noun, meaning 'the result' or 'the outcome'. The sentence about lighting changing how a room feels needs a verb describing an influence happening, so 'affect' is correct there. Swapping in 'effect' as a verb is wrong here because 'effect' as a verb has a narrow, different meaning — 'to effect' something means 'to bring it about or cause it to happen' (as in 'effect a change'), which does not fit describing lighting influencing a feeling. The two sentences that talk about 'the affect' and 'studied the affect' both need the noun for a result, which is 'effect', not 'affect' — 'affect' as a noun is a specialised psychology term for a person's visible emotional expression, not the everyday word for 'result' those sentences are reaching for.
Source: Merriam-Webster: 'Affect' vs. 'Effect'; BBC Bitesize commonly confused words guidance