The developmental trend in many fields of contemporary science is toward integrated general theories. These trends are viewed as essential components of the nature of science rather than expressions of arbitrary preferences of scientists. The law-like factors which lead science toward reliance on general theories include empirical as well as rational components. A model is proposed which exhibits the balance of the relevant factors as calling for increasing use of theories the primitive terms of which are progressively more abstract and (...) general, though no less precise and empirically adequate. (shrink)