Mill, John Stuart (1806–73)

DOI: 10.4324/9780415249126-DC054-2
Version: v2,  Published online: 2005
Retrieved May 21, 2024, from

4. ‘Psychologism’ and naturalism

Mill is often mistakenly accused of ‘psychologism’ in his treatment of logic - an accusation which seems to go back to Husserl (and one which Frege does not make). ‘Psychologism’ is the view that laws of logic are psychological laws concerning our mental processes; or that ‘meanings’ are mental entities, and that ‘judgments’ assert relationships among these entities. But Mill’s view, as we have seen, is that logic and mathematics are the most general empirical sciences, governing all phenomena. He explicitly holds that the distinction between necessary and contingent truths, understood ‘metaphysically’, is empty. And he dismisses the Conceptualist claim that names refer to ideas and propositions express or assert a psychological relation between them.

What explains, then, the attribution of ‘psychologism’ to Mill? Husserl quotes a passage from An Examination of Sir William Hamilton’s Philosophy (1865a), which has been cited many times since:

Logic is not the theory of Thought as Thought, but of valid Thought; not of thinking, but of correct thinking. It is not a Science distinct from, and coordinate with Psychology. So far as it is a science at all, it is a part, or branch, of Psychology; differing from it, on the one hand as the part differs from the whole, and on the other, as an Art differs from a Science. Its theoretic grounds are wholly borrowed from Psychology, and include as much of that science as is required to justify the rules of the art.

(1865a: 359; italics show portion quoted by Husserl)

To give this a psychologistic reading is to take it out of context. Mill means that the logician must formulate rules of reasoning in a manner which will be as helpful as possible to inquirers, and must draw on the psychology of thought to do so. It is in that sense that the art of the logician borrows from the science of the psychologist. How best to promote the art of clear thinking is a psychological question. None the less,

the laws, in the scientific sense of the term, of Thought as Thought - do not belong to Logic, but to Psychology: and it is only the validity of thought which Logic takes cognizance of.

(1865a: 359)

So it is wrong to accuse Mill of psychologism about logic. But there is a sense in which his view of our most basic forms of inductive reasoning is psychologistic, or naturalistic. For how does he respond to the Kantian claim that the very possibility of knowledge requires that there be a priori elements in our knowledge? Even if we accept his inductive account of logic and mathematics, must we not accept the principle of induction itself as a priori?

For Mill, the primitive form of reasoning - in both the epistemological and the aetiological sense - is enumerative induction, the disposition to infer that all As are B from the observation of a number of As which are all B. (Or to the conclusion that a given percentage of all As are B from the observation of that percentage of Bs among a number of As.) We spontaneously agree in reasoning that way, and in holding that way of reasoning to be sound. This method of reasoning, enumerative induction, is not a merely verbal principle. So it cannot on Mill’s own account be a priori. Mill says that we learn ‘the laws of our rational faculty, like those of every other natural agency’, by ‘seeing the agent at work’. We bring our most basic reasoning dispositions to self-consciousness by critical reflection on our actual practice. He is right to say that this reflective scrutiny of practice is, in a certain sense, an a posteriori process. It examines dispositions which we have before we examine them. Having examined our dispositions, we reach a reflective equilibrium in which we endorse some - and perhaps reject others. We endorse them as sound norms of reasoning. There is nothing more to be said: no further story, platonic or transcendental, to be told.

Unlike Hume, or even Reid, Mill shows no interest at all in scepticism. If one thinks that scepticism is both unanswerable and unserious this may be true philosophic wisdom. But to Mill’s epistemological critics, whether they were realists or post- Kantian idealists, it seemed obvious that it was evasion, not wisdom. Naturalism could only seem to differ from scepticism by being uncritical, and in this we find the truth in the allegation that Mill’s system of logic is ‘psychologistic’; if it is sound criticism, it is sound criticism of all naturalistic epistemology.

Citing this article:
Skorupski, John. ‘Psychologism’ and naturalism. Mill, John Stuart (1806–73), 2005, doi:10.4324/9780415249126-DC054-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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