A Man whose height is four feet is short; adding one tenthof an inch to a short man's height leaves him short; therefore, a man whose height is four feet and one tenth of an inch is short. Now begin again and argue in the same pattern. A man whose height is four feet and one tenth of an inch is short; adding one tenth of an inch to a short man's height leaves him short; therefore, a man whose height (...) is four feet and two tenths of an inch is short. In this way, it seems, we can reach the absurd result that a man whose height is four feet plus any number of tenths of an inch is short. For, if the first argument is sound, so is the second; and if the second, so is the third; and so on. There appears to be no good reason for stopping at any one point rather than at another; it is hard to see why the chain of arguments should ever be broken. But the conclusion is ridiculous; it is, for example, preposterous to say that a man whose height is seven feet is, nevertheless, short. (shrink)

This exploration of a notorious mathematical problem is the work of the man who discovered the solution. Written by an award-winning professor at Stanford University, it employs intuitive explanations as well as detailed mathematical proofs in a self-contained treatment. This unique text and reference is suitable for students and professionals. 1966 edition. Copyright renewed 1994.

It is a paradox, whose importance familiarity fails to diminish, that the most highly developed and useful scientific theories are ostensibly expressed in terms of objects never encountered in experience. The line traced by a draughtsman, no matter how accurate, is seen beneath the microscope as a kind of corrugated trench, far removed from the ideal line of pure geometry. And the “point-planet” of astronomy, the “perfect gas” of thermodynamics, or the “pure species” of genetics are equally remote from exact (...) realization. Indeed the unintelligibility at the atomic or sub-atomic level of the notion of a rigidly demarcated boundary shows that such objects not merely are not but could not be encountered. While the mathematician constructs a theory in terms of “perfect” objects, the experimental scientist observes objects of which the properties demanded by theory are and can, in the very nature of measurement, be only approximately true. As Duhem remarks, mathematical deduction is not useful to the physicist if interpreted rigorously. It is necessary to know that its validity is unaltered when the premise and conclusion are only “approximately true.” But the indeterminacy thus introduced, it is necessary to add in criticism, will invalidate the deduction unless the permissible limits of variation are specified. To do so, however, replaces the original mathematical deduction by a more complicated mathematical theory in respect of whose interpretation the same problem arises, and whose exact nature is in any case unknown. (shrink)