An associative structure describes the type of bond that connects  two distinct mental states.[15]  An example of such a structure is the  associative pair  salt/pepper.[16]  The associative structure is defined, in the first instance, functionally: if X and Y form an associative structure, then, ceteris paribus, activations of mental state X bring about mental state Y and vice versa without the mediation of any other psychological states (such as an explicitly represented rule telling the system to activate a concept because its associate has been  activated).[17] In other words, saying that two concepts are associated amounts to saying that there is a reliable, psychologically basic causal relation that holds between them—the activation of one of the concepts causes the activation of the other. So, saying that someone harbors the structure  salt/pepper amounts to saying that activations of salt will cause activations of  pepper (and vice versa) without the aid of any other cognitive states.