The Rational and The Reasonable

Abstract

The existence of two adjectives, ‘rational’ and ‘reasonable’, both derived from the same noun, and designating a conformity with reason, would pose no problem if the two terms were interchangeable. But, most often, it is not so. We understand the expression rational deduction as conformity to the rules of logic, but we cannot speak of a reasonable deduction. On the contrary, we can speak of a reasonable compromise and not of a rational compromise. At times the two terms are applicable but in a different sense: a rational decision can be unreasonable and vice versa. In certain cases the rational and the reasonable are in precise opposition. Parmenides’ theses on being, by seeking to eliminate all incoherence from opinions which common sense entertains in relation to this subject, ends in conclusions which can be presented as rational but which certainly are not reasonable. If Wittgenstein is right in affirming (On Certainty, 261) that there are things that a reasonable man cannot doubt (e.g., that for a time the earth existed), that a reasonable doubt cannot be arbitrary because it must have a foundation (Ibid., 323), then Descartes’ methodical and above all hyperbolical doubt, given as rational, is certainly unreasonable because it would demand an abstention, a refusal to accept, every time we are not compelled by the self-evidence of a proposition. Professor Raleigh rebels against the attitude of William Godwin — the anarchist disciple of Jeremy Bentham — who tries to control all the most human sentiments by the mechanism of the intellect and who seriously maintains that he is wrong to love his father more than other men, unless he is able to prove that his father is better than these other men.¹

Lecture delivered at the International Symposium on ‘Rationality To-day’ held at the University of Ottawa in October 1977. Proceedings published by the University of Ottawa Press, 1979, pp. 213–224.