Every science, like every person, has a duty toward its neighbors, not perhaps to love them as itself, but still to lend them its tools, to borrow tools from them, and, generally, to keep the neighboring sciences straight. We may perhaps judge of the importance of an advance in any one science in terms of the changes which this advance compels the neighboring sciences to make in their methods and in their thinking. But always there is the rule of parsimony. The changes which we in the behavioral sciences may ask for in genetics, or in philosophy, or in information theory must always be minimal. The unity of science as a whole is achieved by this system of minimal demands imposed by each science upon its neighbors, and—not a little—by the lending of conceptual tools and patterns which occurs among the various sciences.