A Google-generated definition of rule as regulations or principles governing conduct in certain scenarios of spheres of activity.

“Reading a book on ethics is, for a scientific mind, a source of great astonishment. The systems are innumerable but the conclusions are alike. Whether the system of ethics treated be religious or utilitarian, whether it be finalistic or pragmatic, it leads invariably to an ensemble of very precise rules, which are, with very few variations, a humanized code for our civilized world.

As for the method which evolved these laws—almost always being peculiar to the social sciences—the line of reasoning begins with concepts which are not very clearly defined. It involves hypotheses which have not been enunciated, and all too often, the true, the beautiful, the good—undefined or undefinable entities—interpose at each step to lead it wherever one may wish to go. Why does the geometrician—the mind of the physicist—feel he steps on quicksand the moment he enters the realm of the moralist? If the rules of morals are one, why are the systems of ethics without number?”

— Jacques Rueff (1922), From the Physical to the Moral Sciences [1]

“In practice different processes differ greatly in degree of irreversibility; but it is a universal rule that if any isothermal process is to occur with finite velocity, it is necessary that a –ΔG > w’. [This applies to] a chemical process which is in some way harnessed for the production of useful work. In the far more common case of a reaction which runs freely, like the combustion of a fuel, or the action of an acid upon a metal; in other words, systems which are subject to no external forces except a constant pressure [exerted by the atmosphere]. In such cases w’ = 0, and it follows that no actual isothermal processes is possible unless: ΔG < 0.”

— Gilbert Lewis (1923), Chemical Thermodynamics and the Free Energy of Chemical Substances [2]

“It can be shown that in all cases, that human molecules rise and fall within the class into which they are born, in a manner which fits the hypothesis that they do so because of their relative aptitudes; and it can also be shown, second, that they rise and fall across the boundary lines of their class in the same manner. This rise and fall into higher and lower classes as a rule takes more than one generation. These molecules are therefore families [see: family molecule] rather than individuals. And this explains why observers who focus attention on individuals so frequently fail to find any relation between ability and class position.”

— Joseph Schumpeter (1942), Capitalism, Socialism, and Democracy

“If the rule you followed brought you to this, of what use was the rule?”

— Joel Coen and Ethan Coen (2007), Dialog: Anton Chigurh to Carson Wells, in No Country for Old Men