Necessary»Sufficient»Contributory cause

A cause is said to be a necessary cause of something if an effect (y) cannot happen unless factor (x) is present. For example, having at least a certain degree of knowledge of the piano keyboard is a necessary condition to play the piano coherently. Note that whilst one must possess this certain degree of keyboard knowledge to play other necessary factors must also be present in order for playing to occur, for example, one must have a desire or inclination to play or at least a tolerance to do so – if both of one’s arms are in non-flexible plaster casts with only the very tips of one’s fingers protruding this may well prevent one’s playing even though all other necessary conditions are met for playing to occur.

A cause is said to be a sufficient cause of something if an effect (y) always occurs when factor (x) is present. For example, grabbing a hot iron (which is exposed and not insulated in any way) is a sufficient condition for burning oneself, but it is not a necessary condition for burning oneself in that one can be burned in a number of ways and grabbing a hot iron is just one amongst these:

Grabbing a hot iron

Touching a hot stove

Scalding oneself with boiling water

Letting a lighted match burn to one’s fingers

et cetera

A contributory cause is one amongst many factors (x) which causes a particular result (y), for example, smoking heavily is a contributory cause of lung cancer – it is not a necessary cause since there are other sources of lung cancer, it is not a sufficient cause since not all such smokers suffer lung cancer.

(see: Probabilistic principle)

To recap:

If x does not happen, y will not happen – necessary cause or condition

If x happens, y will happen – sufficient cause or condition

If x happens, y may happen – contributory cause or condition

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