A system that will usually provide a shortcut to a correct answer. Opposed to algorithms, which will always reach a correct answer, but usually take longer.

To illustrate, an algorithm for an anagram could test every possible combination of letters, and could also cut out letter combinations that never occur in English. This could take a long time. A heuristic user could cut out letter combinations that almost never occur, and might look for certain combinations first.

Humans nearly always use heuristics. You will solve the anagram YBO without sorting through all six possibilities. You can probably use a simple heuristic on TH2YENRVEIG to cut through over 30 million possibilities in a matter of seconds. On the other hand, you might be slowed down by one of your heuristics with IPMHYLOD, as there is an unusual letter combination in the word.

Most math is done by algorithms; for example, adding the digits of a number to see if they are divisible by nine is an algorithm, as it will always work.

Heuristics are commonly known as rules of thumbs.

In a computer science context, a heuristic is a method to reach a result that has not been proven to be correct, or to always give optimal results (otherwise it would be an algorithm). Heuristics are used because in many cases, the algorithms that do the same task are much slower (especially for NP complete problems), and getting an occasional wrong result, or a not quite optimal one is better than having to wait forever for any result at all. A common heuristic is the usage of pseudoprime numbers in lieu of true primes in many cryptograhic programs like PGP and SSH.

According to Imre Lakatos, Scientific Research Programmes have negative and positive heuristics which are tools governing how scientists "do" science. Positive heuristics tell researchers what they should do, negative heuristics tell scientific researchers what they must not do.

In the world of economics, which is the context in which I have studied philosophy of science, a very important heuristic is "Don't ask people what they want, watch what they do". To ask people what they want is seen as unscientific, as their replies will be structured by what is seen as socially respectable. The punishment for breaking negative heuristics is to be thrown out of the scientific community, socially ostracised, in order to protect the Scientific Research Programme from your pseudoscience. The reward for actively using positive heuristics, theorising and doing experiments, is to achieve greater social status and gain the respect of the scientific community.

Imre Lakatos's contribution was to get away from the idea that the rules governing progress are inherently logical - heuristics are often ideologically determined, practical tools which separate different research programmes. The measure by which they can be judged is not their philosophical or scientific validity, but the success or failure of the scientific research programme as a whole.

Heu*ris"tic (?), a. [Gr. to discover.]

Serving to discover or find out.

 

© Webster 1913.