The view that little in human behavior is absolutely fixed, constant, or invariant. Rather, any given behavior or other outcome has varying degrees of likelihood (probability) of occurring under specific conditions. Part of the reason for this variability in behavioral (and developmental) outcomes-according to PARTheory-revolves around almost inevitable imperfections in theory and measurement. But it also revolves around the presumption that human behavior is to some degree inherently indeterminant (see
indeterminance in human behavior). Unlike
mechanical model theories, probability model theories (such as PARTheory) tend to be written in probabilistic language stating that "perceived parental rejection
tends to be associated everywhere with [specific outcomes or antecedents]." (See
universals;
phylogenetic model)
