Surprisingly a lot of incorrect or incomplete answers here.
Both ‘affect’ and ‘effect’ can be used as a noun or a verb, but ‘affect’ is more commonly used as a verb, and ‘effect’ as a noun. As a verb, ‘to affect’ means ‘to have an influence on’. As a noun, ‘an effect’ is the result of some cause. For instance:
* “Housing prices are strongly **affected** by the desirability of a neighborhood”
* “The desirability of a neighborhood has a strong **effect** on housing prices”
* “Alcohol consumption has a negative **effect** on life expectancy”
* “Alcohol consumption negatively **affects** life expectancy”
In other words, “to affect” basically means “to have an effect on”.
(‘To affect’ actually has another, less common meaning as well, which is something like “to pretend”, as in “John affected a British accent in an attempt to attract women”.)
However, ‘affect’ can be used as a noun as well, and ‘effect’ can be used as a verb. These uses are a bit less common and more formal or jargon-y. As a noun, ‘affect’ is a term often used in psychology, to mean something like “mood” or the behaviors reflecting mood. As in “schizophrenic patients often display a flattened **affect**”. Whereas the verb ‘to effect’ basically means “to cause” or “to bring about”. For instance “the French revolution **effected** great societal change across Europe”.
When used as a verb, the ‘e’ in ‘effect’ is pronounced as in ‘deform’, i.e. an ‘eee’-sound. The word “affect” used as a noun has the emphasis on the first syllable. These differences clearly set them a part from the other uses (e.g. “affect” as a verb has the emphasis on the second syllable).
The confusion of course mostly arises between the verb “to affect”, the verb “to effect” and the noun “an/the effect”, as these are all similar in meaning, having to do with causes and influences. If you don’t understand the differences, then as a last resort you can remember that “affect” is usually used as a verb, and “effect” as a noun. But note that this isn’t always true, so using that rule of thumb will cause you to make mistakes.
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