Whether you like it or not

On p. 57 Malott emphasizes that "An aversive stimulus is one we tend to minimize contact with." This is one of the ways to characterize aversive stimuli without saying that they're things you don't like. The fact is that in most cases we don't like aversive stimuli (which are also often called "punishers"). But that fact is peripheral to the best sort of definition.

In BA-speak, as much as possible we define things functionally, that is, in terms of the functions they have or demonstrate. This is similar to defining things operationally, which is a notion that many of you have run into in your other psychology courses.

To put it simply, we try to define things in terms of what they do, the effects they have on other things, or how they affect behavior. So another way to characterize the aversive stimulus (or "punisher") is to say that it's a stimulus which, if it immediately follows a behavior, has the effect of decreasing the future frequency of that behavior.