Mill, John Stuart (1806–73)

6. Mind and matter

Mill sets out his metaphysical views in An Examination of Sir William Hamilton’s Philosophy. Hamilton was the last eminent representative of the Scottish Common Sense School, and a ferocious controversialist - in Mill’s eyes a pillar of the right- thinking establishment, ripe for demolition. The result is that Mill’s discussion of general metaphysical issues is cast in a highly polemical form which leaves important issues shrouded in obscurity. He does however give himself space to develop his view of our knowledge of the external world.

He begins with a doctrine which he rightly takes to be generally accepted (in his time) on all sides: ‘that all the attributes which we ascribe to objects, consist in their having the power of exciting one or another variety of sensation in our minds; that an object is to us nothing else than that which affects our senses in a certain manner’ (1865a: 6). This is ‘the doctrine of the Relativity of Knowledge to the knowing mind’. It makes epistemology, in Mill’s words, the ‘Interpretation of Consciousness’. He proceeds to analyse what we mean when we say that objects are external to us:

To assign this origin Mill postulates that

Physical objects are ‘Permanent Possibilities of Sensation’. (There is a change in the ‘permanent’ possibilities of sensation whenever there is change in the world. Mill also uses other terms, such as ‘certified’ or ‘guaranteed’.) We often find that whenever a given cluster of certified possibilities of sensation obtains, then a certain other cluster follows. ‘Hence our ideas of causation, power, activity...become connected, not with sensations, but with groups of possibilities of sensation’ (1865a: 181) (see Phenomenalism §1).

However, even if our notion of matter as the external cause of sensations can be explained on psychological principles, it is still possible to hold that good grounds can be given for thinking the notion to have instances. There might be a legitimate inference from the existence of the permanent possibilities and their correlations to the existence of an external cause of our sensations. It is at just this point that Mill’s inductivism plays a part. The inference would be a case of hypothetical reasoning, to an explanation of experience which transcended all possible data of experience; and that is precisely what Mill rejects: ‘I assume only the tendency, but not the legitimacy of the tendency, to extend all the laws of our own experience to a sphere beyond our experience’ (1865a: 187).

If matter is the permanent possibility of sensation what is mind? Can it also be resolved into ‘a series of feelings, with a background of possibilities of feeling’? Mill finds in this view a serious difficulty: to remember or expect a state of consciousness is not simply to believe that it has existed or will exist; it is to believe that I myself have experienced or will experience that state of consciousness.

Thus although Mill is unwilling to accept ‘the common theory of Mind, as a so-called substance’, the self-consciousness involved in memory and expectation drives him to ‘ascribe a reality to the Ego - to my own Mind - different from that real existence as a Permanent Possibility, which is the only reality I acknowledge in Matter’ (1865a: 208).

This ontology, Mill thinks, is consistent with common sense realism about the world. Phenomenalism - the conception of matter as possibility of experience - allegedly leaves common sense and science untouched. In particular, mind and experience is still properly seen as a part of the natural order.

Yet if phenomenalism is right, only the experiences are real. Mill thinks we are led to that conclusion by the very standards of reasoning recognized in a naturalistic ‘science of science’, or ‘system of logic’. If he is right, then the naturalistic vision of the world which sees minds as part of a larger causal order is self-undermining. For if we are led to the conclusion that only states of consciousness are real by an application of naturalism’s own standards, then that conclusion has to be understood on the same level as the naturalistic affirmation that states of consciousness are themselves part of a larger causal order external to them - and therefore as inconsistent with it. Causal relations cannot exist between fictional entities which are mere markers for possibilities of sensation.

This is the fault-line in Mill’s epistemology and metaphysics. Either naturalism undermines itself, or there is something wrong with Mill’s inductivist analysis of our natural norms of reasoning, or with his endorsement of the doctrine of the Relativity of Knowledge, or with both. It is not obvious that Mill’s most fundamental tenet - his naturalistic view of the mind - can be safeguarded by rejecting inductivism and endorsing the hypothetical method. There is still something implausible about hypothesizing the world as an explanation of pure experience. Mill himself explicitly acknowledged that memory, as well as induction, has epistemic authority. Had he analysed the significance of such an acknowledgment more thoroughly, he might have noted a parallel: on the one hand a primitive epistemic norm which warrants assertions about the past based on present memory-experiences; on the other, primitive epistemic norms which warrant assertions about the physical world based on perceptual experience. But perhaps that would have taken him too far in the direction of Reid’s principles of common sense (see Reid, T.).