By reconstructing Mill’s argument, I will show that there is no contradiction between Mill’s determinism and his views on tendency laws. Mill was consistent in his approach. In the context of his deterministic method, he provided adequate explanation of why we should be viewing the phenomena of the world as tendencies, both in the physical and the (mental or moral) social sciences, without negating causality. However, at the same time, Mill outlines the limitations of causality and its laws.
This essay has two parts. In the first part I consider Mill’s tendency laws in the natural sciences, while in the second part I focus on tendency laws in the social sciences.
I have sourced Mill’s original material from ‘System of Logic’ (SOL) and ‘On the Definition of Political Economy and on the Method of Investigation proper to it’ (DPE). Both are included in Nagel (1). In the text I use ‘social science’ to denote Mill’s ‘mental or moral science’, or ‘political economy’.
Part I: The physical sciences
Mill’s determinism is based on ‘the various uniformities of the course of nature, which when ascertained by what is regarded as a sufficient induction, we call he laws of nature’ (SOL, Book III, Chapter IV, § 1; 1, 187). The law of causation dictates that every fact which has a beginning has a cause. He proceeds to define ‘the cause of a phenomenon to be the antecedent, or the concurrence of antecedents, on which it (the phenomenon) is invariably and unconditionally consequent’. (SOL, Book III, Chapter V, § 3; 1, 197-198). The repeating, invariable and unconditional consequence of the phenomenon enables us to generalize, inferring its cause.
A phenomenon will occur again and again, as long as the phenomena comprising its cause occur again, and provided that ‘no other phenomenon having the character of a counteracting cause shall exist’. (SOL, Book III, Chapter V, § 5; 1, 203).
The concept of a counteracting cause is opening the door to tendency laws. It so happens that in some cases: ‘There are often several independent modes in which the same phenomenon could have originated… Many causes may produce mechanical motion; many causes may produce some kinds of sensation; many causes may produce death’. (SOL, Book III, Chapter X, § 1; 1, 239).
Given the multitude of causes in some phenomena, it is possible that diverse causes act simultaneously, in composition; in such case ‘two or more laws interfere with one another and apparently frustrate or modify one another’s operation, yet in reality all are fulfilled’. (SOL, Book III, Chapter X, 4; 1, 246).
Therefore, when a phenomenon may be explained by a multitude of causes and opposing causes occur simultaneously, we cannot be certain about the outcome. This does not mean that the laws are not valid. They are fulfilled, but the outcome of the acting of opposing causes may produce different outcomes. For this reason: ‘All laws of causation, in consequence of their liability to be counteracted, require to be stated in words affirmative of tendencies only, and not of actual results.’ (SOL, Book III, Chapter X, 4; 1, 248).
Part II: The social sciences
In the social sciences we have to cope with two major issues: great complexity and our ignorance, to degrees that are by far higher than in the physical sciences. ‘We study nature… in circumstances… of great complexity and never perfectly known to us, and with the far greater part of the processes concealed from our observation.’ (DPE; 1, p.427).
Causes will operate in a certain manner unless they are counteracted. ‘We may be able to conclude, from the laws of human nature applied to the circumstances of a given state of society, that a particular cause will operate in a certain manner unless counteracted; but we can never be assured to what extent or amount it will so operate, or affirm with certainty that it will not be counteracted; because we can seldom know even approximately, all the agencies which may co-exist with it, and still less calculate the collective result of so many combined elements’. (SOL Book VI, Chapter IX, § 2; 1, 334).
It is impossible to be ‘quite sure that all circumstances of the particular case are known to us sufficiently in detail and that our attention is not unduly diverted from any of them.’ The unknown circumstances, the ones that ‘have not fallen under the cognizance of science, have been called “disturbing causes”’. (DPE; 1, p.429).
We can never be assured to what extent or amount the disturbing causes will operate, or affirm with certainty that a particular cause will not be counteracted. ‘We may be able to conclude, from the laws of human nature applied to the circumstances of a given state of society, that a particular cause will operate in a certain manner unless counteracted; but we can never be assured to what extent or amount it will so operate, or affirm with certainty that it will not be counteracted; because we can seldom know even approximately, all the agencies which may co-exist with it, and still less calculate the collective result of so many combined elements.’ (SOL, Book VI, Chapter IX, § 2; 1, 334).
Having established the existence of disturbing causes, Mill proceeds to preserve the integrity of causality, by claiming that: ‘The disturbing causes have their laws, as the causes which are thereby disturbed have theirs; and from the laws of the disturbing causes, the nature and amount of the disturbance may be predicted “a priori”, like the operation of the more general laws which they are said to modify or disturb, but with which they might more properly be said to be concurrent. The effect of the special causes is then to be added to, or subtracted from, the effect of the general ones.’ (DPE; 1, p.430).
As the last sentence reminds us, what makes all of this line of argumentation valid is the compounding of causes. ‘When an effect depends upon a concurrence of causes, those causes must be studied one at a time, and their laws separately investigated, if we wish, through the causes, to obtain the power of either predicting or controlling the effect; since the law of the effect is compounded of the laws of all the causes which determine it.’ (DPE; 1, p.421).
We have now arrived at the conclusion of the argument. ‘It is evident that the social sciences considered as a system of deductions a priori, cannot be a science of positive predictions, but only of tendencies’. (SOL, Book VI, Chapter IX, § 2; 1, 334). This is the same conclusion Mill arrived at when considering causality in the physical sciences. One might say though, that the tendencies are more evident in the social compared to the physical sciences, due to the higher complexity of the phenomena and our ignorance.
Mill closes the “loop” of the scientific process with verification using the “a posteriori” method. The “a priori” method of investigation is supplemented by the “a posteriori” method as a means of verifying truth and ‘reducing to the lowest point that uncertainty before alluded to as arising from the complexity of every particular case, and from the difficulty (not to say impossibility) of our being assured “a priori” that we have taken into account all the material circumstances.’ (DPE; 1, p.431).
Social phenomena are complex, and there are potentially many disturbing causes, most of which, if not all, we do not know of. Therefore the relevant laws governing the phenomena can only be stated as tendency laws which we verify using the “a posteriori” method. The verification process may give us knowledge about some of the disturbing causes and their laws.
Having shown that Mill was consistent in his approach, I want to conclude by briefly considering the legacy of “tendency laws”.
‘When things are not ceteris paribus, the laws in question still apply. But they now describe tendencies – partial elements of a complex situation. (Therefore) ceteris paribus laws and tendencies go hand in hand – and that seems reasonable enough’ (2). Kincaid’s statement practically attributes the “ceteris paribus” approach to Mill. And many economists and philosophers agree with him. Given the importance of ceteris paribus laws in economics, we can conclude that Mill’s “tendency laws” have played a very important role in the shaping and the development of economics.
However, the limits to our knowledge and understanding of complex phenomena must not be underestimated. As Hayek argues: ‘…we can reasonably claim that a certain phenomenon is determined by known natural forces and at the same time admit that we do not know precisely how it has been produced… It would then appear that the search for the discovery of laws is not an appropriate hallmark of scientific procedure but merely a characteristic of the theories of simple phenomena as we have defined these earlier; and that in the field of complex phenomena the term ‘law’ as well as the concepts of cause and effect are not applicable without such modification as to deprive them of their ordinary meaning.’ (3)
When it comes to complex social phenomena, “tendency laws” may in addition to providing some explanations, reveal the limits of causal determinism, and enhance “our knowledge of our ignorance” (4, quoted by Hayek in 3).
1. Nagel, Ernest. John Stuart Mill’s Philosophy of Scientific Method. Hafner Publishing Company. New York, 1950.
2. Kincaid, Harold. Defending Laws in the Social Sciences, in: Martin, Michael and McIntyre, Lee (eds.) Readings in the Philosophy of Social Sciences. MIT Press, 1994.
3. Hayek, F.A. The Theory of Complex Phenomena, in: Martin, Michael and McIntyre, Lee (eds.) Readings in the Philosophy of Social Sciences. MIT Press, 1994.
4. Popper, K. R. “On the Sources of Knowledge and Ignorance”, Proceedings of the British Academy. 46, 1960.