A model of ethical behaviour and the atomic hypothesis
Keynes's analysis of alternative choices for courses of ethical action amounts to a critique of Moore's model. Moore was concerned with 'the relation of ethics to conduct' in Principia Ethica (Moore, 1903, pp. 146-55), which has a sophisticated utilitarian flavour based on the frequency theory of probability.
Moore's ethical model is an original type or prototype of a classical economist's model of economic behaviour which was stubbornly attacked by Keynes, both in GT and in subsequent publications. It should, therefore, not be neglected by studies of the evolution of Keynes's philosophical thoughts. The target of Keynes's attack is the doctrine of 'mathematical expectations' assumed in Moore's model.
The doctrine explains the situation in which an individual is facing a choice of alternatives from which he or she must choose. The order of degrees of 'mathematical expectations' attached to each alternative course of action represents an 'echelle d'intervalles', as it were, in one's preference. According to this doctrine, one must assume that an individual can forecast the future with certainty. In addition, one must introduce two further assumptions: (a) the degrees of goodness attached to each course of action must be not only numerically measurable but also arithmetically additive, and (b) their degrees of probability must be numerically measurable. According to Keynes, both assumptions stand on a doubtful and unsteady foundation. In particular, assumption (b) runs directly counter to his conception of probability as put forward in TP. In short, the doctrine of 'mathematical expectations' adopted in Moore's ethical model is based on neither firm nor plausible assumptions. Another serious shortcoming is that it overlooks the 'weights' of arguments; this means that it fails to consider the amount of evidence at the basis of each probability and the element of 'risk'.7
The following statement by Keynes relates to the choice of correct action. Interestingly, it seems somewhat similar to his later views.
Thus even if we know the degree of advantage which might be obtained from each of a series of alternative courses of actions and know also the probability in each case of obtaining the advantage in question, it is not always possible by a mere process of arithmetic to determine which of the alternatives ought to be chosen. If, therefore, the question of right action is under all circumstances a determinate problem, it must be in virtue of an intuitive judgement directed to the situation as a whole, and not in virtue of an arithmetical deduction derived from a series of separate judgements directed to the individual alternatives each treated in isolation.
(TP, pp. 344-5, emphasis added)
As described above, Moore's version of ethical behaviour depends on the doctrine of 'mathematical expectations', and it is obviously based on an empirical and frequency theory of probability. This is one of the reasons why Keynes tries to reject the frequency theory. Keynes sums up the importance of his own conception of probability thus:
Probability begins and ends with probability. ... The proposition that a course of action guided by the most probable considerations will generally lead to success, is not certainly true and has nothing to recommend it but its probability.
The importance of probability can only be derived from the judgement that it is rational to be guided by it in action; and a practical dependence on it can only be justified by a judgment that in action we ought to act to take some account of it. It is for this reason that probability is to us the 'guide of life'.
(TP, p. 356)
What needs to be emphasized here is that, while the 'universe' view forms a sort of scheme in which Keynes considers the model of ethical behaviour, he seems to grasp such a 'universe' in virtue of its dependence upon the atomic hypothesis. Here it should be noticed that Moore expressed the difficulty associated with the decision of alternative courses of action thus: 'the first difficulty in the way of establishing a probability that one course of action will give a better total result than another, lies in the fact that we have to take account of the effect of both throughout an infinite future' (Moore, Principia Ethica, p. 152; TP, p. 341; emphasis added).
It is worth pointing out Keynes's caution against this difficulty suggested by Moore. Keynes states
The difficulties which exist are not chiefly due, I think, to our ignorance of the remote future. The possibility of our knowing that one thing rather than another is our duty depends upon the assumption that a greater goodness in any part makes, in the absence of evidence to the contrary, a greater goodness in the whole more probable than would the lesser goodness of the part. We assume that the goodness of a part is favourably relevant to the goodness of the whole. Without this assumption we have no reason, not even a probable one, for preferring one action to any other on the whole. If we suppose that goodness is always organic, whether the whole is composed of simultaneous or successive parts, such an assumption is not easily justified. The case is parallel to the question, whether physical law is organic or atomic, discussed in chapter 21.
(TP, pp. 342-3, my emphasis)
Whether an increase in the goodness or advantage of any 'part' contributes to the increase in goodness for the 'whole' of society, such a problem requires as a sine qua non condition the atomic hypothesis in order that a positive or favourable parts-whole relation could be established. This does not mean that the goodness of the units ought to be exhaustively atomistic; it may be as well to suppose that 'the units whose goodness we must regard as organic and indivisible are not always larger than those the goodness of which we can perceive and judge directly' (TP, p. 343).