Cognitive Dissonance is one of the most interesting and applicable psychlogical princples. It can be used to explain and influence a wide variety of human behaviour.

Let's start with the words:

Cognitive - To do with the mind

Dissonance - A mis-match, sounds which clash, disagreement between two entities.

Cognitive Dissonance - A discrepancy between beliefs or between beliefs and actions. A typical examples given is the following scenario:

You do a lot of long journeys by road, so you buy a nice, new car for a large amount of money. Unfortunately you find the seats uncomfortable.

Now, when you bought the car, you thought it was a good choice, worth all that money. But the fact that it is uncomfortable implies that it is a bad choice. You are in a state of Cognitive Dissonance.

The theory says that something has to give, belief or action.

Now it's hard to undo your action of buying the car, if you resell it then you'd have to admit that you're a fool and that you wasted your money.

The alternative is to find other reasons to justify your choice. So you concentrate on the good things about the car, perhaps it looks particularly sporty, or has great fuel efficiency. You can then believe you bought it for these reasons.

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• http://www.propaganda101.com/cognitiv.htm - includes description of an early experiment by Festinger and Carlsmith

• http://tip.psychology.org/festinge.html

• See also: lists of logical fallacies http://www.propaganda101.com/logical.htm http://nwc.hccs.cc.tx.us/govt/fallacy.asp http://webpages.shepherd.edu/maustin/composition/fallacies.htm