[jyl]

Effect means the result of some influence or action. Action X produces effect Y.

Affect can mean largely the same thing.

However, affect has another meaning related to psychology. A person has no affect if he shows no response, usually emotional, to some stimulus. Used here, the emphasis is on the "af" syllable.

A better explanation, which explains some nuances that I missed above -

"There are five distinct words here. When “affect” is accented on the final syllable (a-FECT), it is usually a verb meaning “have an influence on”: “The million-dollar donation from the industrialist did not affect my vote against the Clean Air Act.”

Occasionally a pretentious person is said to affect an artificial air of sophistication. Speaking with a borrowed French accent or ostentatiously wearing a large diamond ear stud might be an affectation. In this sort of context, “affect” means “to make a display of or deliberately cultivate.”

Another unusual meaning is indicated when the word is accented on the first syllable (AFF-ect), meaning “emotion.” In this case the word is used mostly by psychiatrists and social scientists—people who normally know how to spell it.

The real problem arises when people confuse the first spelling with the second: “effect.” This too can be two different words. The more common one is a noun: “When I left the stove on, the effect was that the house filled with smoke.” When you affect a situation, you have an effect on it.

The less common is a verb meaning “to create”: “I’m trying to effect a change in the way we purchase widgets.” No wonder people are confused. Note especially that the proper expression is not “take affect” but “take effect”—become effective. Hey, nobody ever said English was logical: just memorize it and get on with your life.

The stuff in your purse? Your personal effects.

The stuff in movies? Sound effects and special effects."