Is it "affect" or "effect"?

Contexti

This is the single most-searched grammar question in English — it has been the top "commonly confused words" query on Google every year since search-trends data have been public. The pair trips up confident writers because both words exist in both grammatical slots, just rarely.

A little moreii

The quick test: can you put "the" in front? The effect works; the affect usually does not. Another test: if the word is the action of the sentence, it is almost always affect; if it is the thing left behind, it is effect.

Examplesiii

Watch foriv

The full entryv

More quick answersvi

• → Is "affect" a verb? Yes. "Affect" is almost always a verb, meaning to influence or change something: the weather affected our plans.
• → Is "effect" a noun? Yes. "Effect" is almost always a noun — the result of something: the effect was immediate.
• → Is it "deeply affected" or "deeply effected"? "Deeply affected." The word describes an action done to someone — that's the verb affect.
• → Is it "side affects" or "side effects"? "Side effects." The side things are results, not actions — that's the noun effect.