Essays on some unsettled Questions of Political Economy · John Stuart Mill
ESSAY V.
Thus if it were stated to be a law of nature, that all heavy bodies fall to the ground, it would probably be said that the resistance of the atmosphere, which prevents a balloon from falling, constitutes the balloon an exception to that pretended law of nature. But the real law is, that all heavy bodies _tend_ to fall; and to this there is no exception, not even the sun and moon; for even they, as every astronomer knows, tend towards the earth, with a force exactly equal to that with which the earth tends towards them. The resistance of the atmosphere might, in the particular case of the balloon, from a misapprehension of what the law of gravitation is, be said to _prevail_ over the law; but its disturbing effect is quite as real in every other case, since though it does not prevent, it retards the fall of all bodies whatever. The rule, and the so-called exception, do not divide the cases between them; each of them is a comprehensive rule extending to all cases. To call one of these concurrent principles an exception to the other, is superficial, and contrary to the correct principles of nomenclature and arrangement. An effect of precisely the same kind, and arising from the same cause, ought not to be placed in two different categories, merely as there does or does not exist another cause preponderating over it.
It is only in art, as distinguished from science, that we can with propriety speak of exceptions. Art, the immediate end of which is practice, has nothing to do with causes, except as the means of bringing about effects. However heterogeneous the causes, it carries the effects of them all into one single reckoning, and according as the sum-total is _plus_ or _minus_, according as it falls above or below a certain line, Art says, Do this, or Abstain from doing it. The exception does not run by insensible degrees into the rule, like what are called exceptions in science. In a question of practice it frequently happens that a certain thing is either fit to be done, or fit to be altogether abstained from, there being no medium. If, in the majority of cases, it is fit to be done, that is made the rule. When a case subsequently occurs in which the thing ought not to be done, an entirely new leaf is turned over; the rule is now done with, and dismissed: a new train of ideas is introduced, between which and those involved in the rule there is a broad line of demarcation; as broad and _tranchant_ as the difference between Ay and No. Very possibly, between the last case which comes within the rule and the first of the exception, there is only the difference of a shade: but that shade probably makes the whole interval between acting in one way and in a totally different one. We may, therefore, in talking of art, unobjectionably speak of the _rule_ and the _exception_; meaning by the rule, the cases in which there exists a preponderance, however slight, of inducements for acting in a particular way; and by the exception, the cases in which the preponderance is on the contrary side.
Ideas discussed in this chapter
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