Conditioning and Contingency I've learned, that spatiotemporal neighborhood among the conditioned and the unconditioned stimuli is a presupposition of conditioning (classical or operant). A second presupposition is called "contingency" in my notes. The explanation is, that the CS has to predict the US with certainty. But in my opinion the meaning of the word "contingency" is quite the opposite of predictability with certainty (necessity). Why is the second presupposition called "contingency"?
"Contingent" means "dependent upon".

See the first definition of
http://dictionary.reference.com/browse/contingent?s=t

The reason the second definition there (which is the one you are thinking of) has the same word is because if B is contingent on A, then B is not for sure going to happen.  B will only happen if A does.