has presented the following argument against what he calls the 'orthodox' view that in the ordinary sense of 'if-then', p=q does not entail that if p then q. (Clark credits Geoffrey Hunter as the source of the argument.)
It is arguable that, in general, if p, q entail r, then p entails that if q then r. I would not wish to defend the converse of this, but it seems difficult to reject the claim in the stated direction. Maybe it is in need of some qualification; but, even if it is, that qualification may not impugn the validity of the following argument. It is uncontroversial that p D q, p entail q. But by the general principle just affirmed, it follows that p ~ q entails that ifp then q.1 John J. Young has challenged Clark's argument on the grounds that he has given no good reasons for accepting the principle that if p, q entail r, then p entails that if q then r. 2 According to Young, the force of the principle "seems to arise from its resemblance to the deduction theorem encountered in the propositional calculus" (p. 57). After showing that this resemblance is only superficial, Young concluded that we need not accept the principle until some favorable evidence is forthcoming. One would have thought, however, that the principle, which is a variation on the well-known Principle of Exportation, is sufficiently plausible in itself to have made Young feel constrained to present some arguments against it. I will attempt to show that while the principle in its stated form can indeed be discredited, certain qualified versions of it seem at once difficult for the 'orthodox' theorist to reject and capable of lending at least some support to Clark's argument.
- Since it seems that p, q entail p, while, as the "orthodox' theorists have emphasized, it seems that p does not entail that if q then p, it appears that Clark's principle, (i) If p, q entail r, then p entails that if q then r,