For clarity of understanding, it is useful to couch a theory in terms of stable principles which lay out the constraints upon, and expectations for, the theory. Here there are three: What empowers an organism; what constrains it; and what directs it—the engine, the brakes, and the steering wheel of the vehicle of behavior. This theory concerns the behavior of nonverbal organisms, and verbal ones when their minds are not engaged. What empowers organisms are incentives (i.e., potential reinforcers) that arouse them. Incentives arouse many behaviors, which compete for expression both with themselves, and with other kinds of responses. Thus embroiled, what is an organism to do? The agitation is likely to expose affordances in the environment (i.e., potentials for action) that attract the organism and its responses. In laboratory environments, these constitute discrete stimuli that are signs of reinforcers—incentives available via operant responses. These simple notions direct a theory, grounded in substantiating data: the arousal engendered by incentives is proportional to their rates of presentation, with the constant of proportionality depending on the needs of the organism. The emission of responses depends on the remaining time available, given responses of the same and different classes. Direction is given by Thorndike’s Principle: animals approach satisfiers—goals that coordinate with their needs. These simple principles birth quantitative models that describe many of the phenomena studied in the field known as Behavior Analyses, and beyond.