Biologists make general simplified statements about living organisms, Chemists make simplified statements about how atoms interact with each other, and Sociologists make simplified statements about how groups of people interact with each other. While simplification does make nature easier to understand, it by necessity means that some things about the subject matter get dropped out of the analysis. For most of us, we might talk about how beautiful it is, etc. Beauty is one of those characteristics that is subjective , and therefore beyond a scientific analysis. Such reluctance on the part of a biologist makes a Rosella no less beautiful to the biologist, it's just that subjective analysis is outside of the boundaries that biologists impose on themselves when they are talking about a scientific analysis of living organisms.
General principles are statements of lawful relationships between parts of nature.
These general principles, if they are to have much value, are at a level of abstraction that they are postulated relationships called hypothetical constructs . In the case of a science of behavior, the lawful relationships under scrutiny are between observable behavior and changes in the environment. Other processes, such as thinking, feeling, etc. may be going on, but they are inaccessible, and therefore beyond a scientific analysis. Behaviorists are not claiming that their analysis is the total definition of human nature, but an attempt to understand behavior in the manner that any scientific analysis does. A scientific analysis assumes that, within the confines of our inherited predispositions, we are the products of our interaction with our environment.