n. a conditional, probabilistic relation between two events. When the probability of Event B given Event A is 1.0, a perfect positive contingency is said to exist. When Event A predicts with certainty the absence of Event B, a perfect negative contingency is said to exist. Probabilities between –1.0 and 1.0 define a continuum from negative to positive contingencies, with a probability of zero indicating no contingency. Contingencies may be arranged via dependencies or they may emerge by accident (see accidental reinforcement). See also law of contiguity; reinforcement contingency.