Mr Ross is, of course, perfectly well aware of the necessity of offering some answer on this matter. On p. 23 the difficulty is explicitly raised. It may be objected, he says, 'that our theory that there are these various and often conflicting types of prima facie duty leaves us with no principle upon which to discern what is our actual duty in particular circumstances.' What, then, is his answer?
We may begin by considering briefly the answer which follows immediately upon the statement of the difficulty, although we do not here, I think, have Mr Ross's whole mind on the matter.
Mr Ross points out first of all that what he calls 'the rival theory' - Mr Moore's 'ideal utilitarianism' - is not in a position to urge the present objection. For it is in a like case. 'When we have to choose between the production of two heterogeneous goods, say knowledge and pleasure, the "ideal utilitarian" theory can only fall back on an opinion, for which no logical basis can be offered, that one of the goods is the greater'.
This, I think, is true. But we must not forget that the appointment of ideal utilitarianism as 'the rival theory' rests upon the discretion of Mr Ross - not upon any agreed characteristic of the nature of ethical science. Most people would be prepared to allow that there are other 'rival theories,' and at least some of these do not, with ideal utilitarianism, accept a plurality of ultimate goods, and therefore are not saddled with this disability of having no single standard to which to refer in cases of conflict. Not, of course, that it is always, or even often, easy to apply in practice the standard of a monistic ethics with confidence in the accuracy of one's results. As Mr Ross says, when 'we consider the infinite variety of the effects of our actions in the way of pleasure,' it is evident that even hedonism offers no 'readily applicable standard of right conduct.' But it is one thing to have no 'readily applicable' standard, another thing to have no 'standard' at all, but rather many 'standards,' each equally authoritative. The former is a disability pertaining perhaps to all ethical systems; but all ethical systems do not share with ideal utilitarianism and (it may be) Mr Ross's theory the latter disability.
Even as an argumentum ad hominem, then, this point has only a limited effectiveness. But Mr Ross, in any event, professes himself unwilling to be content with an argumentum ad hominem. (After all, a theory is not really made more tenable by the fact that its defects are shared by opposing theories.) 'I would contend,' he goes on to say, 'that in principle there is no reason to anticipate that every act that is our duty is so for one and the same reason.' If, after reflection, prima facie duties, like keeping a promise and redressing an injury, do not appear reducible to one another, we are not entitled on any a priori ground, he urges, to assume that such a reduction is possible.
The exact significance of this contention does not seem to me to be altogether clear. Mr Ross is replying to the objection that on his theory we are left with no principle by which to discover our actual duty in cases where prima facie duties prescribe mutually exclusive courses. Is he admitting that he has no such principle, and alleging that there is no a priori ground for supposing that there should be one? Or is he saying only that he has not, and that there is no a priori reason why he should have, a principle of the kind sponsored by monistic moral theories - leaving open the question of whether there is or is not some kind of principle to which appeal may be made on his theory?
I think we may take it that the second is Mr Ross's real meaning. The passage under consideration, with its context, certainly suggests the former, more sceptical meaning, but it is not, I think, definitely incompatible with the latter meaning. And although at this juncture the subject is abruptly discontinued, later parts of the chapter seem to make it clear that for Mr Ross there is a principle of sorts to which we can refer for the determination of our 'actual' duty. As is surely, indeed, very necessary - even a priori necessary, if ethics is to be possible at all. There cannot be a 'science of right and wrong' if there just is not any intelligible principle upon which we can ever decide what is our actual duty.
What, then, is the principle of 'actual' or 'absolute duty' to which we may refer for the settlement of conflicts between prima facie duties? Mr Ross's answer is, as I understand it, that we have to consider which of our possible acts will produce the greatest balance of prima facie Tightness over prima facie wrongness. We 'must reflect to the best of our ability on the prima facie rightness or wrongness of various possible acts in virtue of the characteristics we perceive them to have' (p. 32), for 'right acts can be distinguished from wrong acts only as being those which, of all those possible to the agent in the circumstances, have the greatest balance of prima facie rightness, in those respects in which they are prima facie right, over their prima facie wrongness, in those respects in which they are prima facie wrong '(p. 41).