Knowing when to use “affect” or “effect” is a real stumbling block for many people.
Generally (though not always, which I shall come to later), affect is a verb and effect is a noun.
The definition of affect is “to have an influence on someone or something, or to cause a change in someone or something”.
I came across a great way to remember this – think of the word affectionate. That’s an emotion, a feeling.
So if something is having an impact on emotions or feelings, it affects you.
(Of course, this does also apply to situations, not just emotions and feelings. Pollution affects the state of the oceans.)
The definition of effect is “the result of a particular influence”.
As noted on dictionary.com, since effect can also mean a result, or a consequence, just swap out the word effect with one of these alternatives. “Not having breakfast resulted in her hunger” changes to “the effect of not having breakfast was being hungry.”
So – eating breakfast affects someone’s hunger (because eating breakfast has an impact on a feeling or sensation).
But eating breakfast has the effect of ridding hunger (because it has a result).
Why are they so similar?
Because they both derive from the Latin facere – “to do, make”.
Affect derives from the Latin afficere – “to act upon, influence”.
Effect derives from the Latin efficere – “to bring about, do”.
Which possibly doesn't help too much, and if you take on board all this information it will only confuse matters!
And confusion can also kick in when effect is used as a verb, “to make happen”, eg, “to effect change”.
If you effect change, you are bringing change about.
But if this is all too much, just stick to the definitions and examples at the top of the page.
Affect – verb – having an impact on something.
Effect – noun – the result or consequence of something.