Generally,
affect as a verb means
to influence;
effect however is usually the noun resulting from this influence.
Incorrect: Farmers wonder how the drought will effect this year’s crops.
Correct: Farmers wonder how the drought will
affect this year’s crops.
Correct: Farmers wonder what
effect the drought will have on this year’s crops.
Effect can also be a verb meaning
to bring about.
Affect can also be a noun, but it is used strictly in psychological contexts.
An
affect or
affectation is usually an assumed or false mannerism (think of some poseur lovey-dovey crops walking up and down quoting Proust to each other); but an effect (effectation doesn't exist) is a
real and tangible result (think of crops sweating and rotting in the heat).
I think this gives a good distinction between these two words that are very much a stylistic bugbear.
Re: Affect vs. Effect 
Linear Mode
