I follow quite a few language-y blogs and I’m always amused by prescriptive grammarians outraged by ‘incorrect’ language use, such as people writing the wrong homophone: ‘their’ instead of ‘there’ or ‘effect’ instead of ‘affect’. I imagine most people know when to use one instead of the other, but just typo the wrong one, so I don’t see the need to criticise.
The general rule of thumb is that affect is a verb and effect is a noun. I usually taught pupils to remember that A (for affect) comes before E (for effect) in the alphabet and an action (affect) usually comes before a result (effect); for example ‘The sugar affected the taste of the tea, the effect was that it was too sweet’.
However the affect = verb and effect = noun this isn’t always true.
In the past, affect and effect both had a lot more meanings than they do today (some of which are still in use) so people irate at their abuse should be thankful they have less meanings now!
In the past affect could be used as noun with a variety of meanings; for example, being in favour of someone, an emotional response, an inner disposition, or a disease. It could be used as an adjective to mean ‘inclined’. Along with its common use today as a verb to mean having an effect on something, it could also mean to aspire to, affection for, having artificial manners, or to have a tendency towards something.
Effect also had numerous meanings over the yeas. For example, as a noun to mean an outward manifestation, an accomplishment, or the impression produced by a work of art, along with the common meaning of ‘results’. It can also today be a verb meaning to bring about an event.
This last example is shown in this cartoon my boyfriend sent me, which I love!