John Stuart Mill (1806-1873) was, like Comte, a Platonist in the sense of valuing knowledge chiefly as an instrument of social reform. He was indeed bred up by his father, James Mill (1773-1836), and by Jeremy Bentham as a prophet of the new Utilitarianism as Comte was, to some extent, trained by St. Simon to substitute a new order for that which the Revolution had destroyed. Mill, however, had been educated on the lines of Greek liberty rather than in the tradition of Roman authority; while both were largely affected by the Romanticism current in their youth. The worship of women, revived from the age of chivalry, entered into the romantic movement; and it may be mentioned in this connection that Mill calls Mrs. Taylor, the lady with whom he fell in love at twenty-four and married eighteen years later, "the inspirer and in part the author of all" that was best in his writings; while Comte refers his religious conversion to Madame Clotilde de Vaux, the object of his adoration in middle life. It seems probable, however, from the little we know of Mrs. Taylor—whom Carlyle credits with "the keenest insight and the royallest volition"—that her influence was the reverse of Clotilde's. If anything, she attached Mill still more firmly to the cause of pure reason.
It has been mentioned how Kant's metaphysical
agnosticism was played out by Hamilton against Cousin. A little later Whewell, the Cambridge historian of physical science, imported Kant's theory of necessary truth in opposition to the empiricism of popular English thought, and Kant's Categorical Imperative in still more express contradiction to Bentham's utilitarian morality. Now Mill, educated as he had been on the associationist psychology and in the central line of the English epistemological tradition, rejected the German apriorism as false in itself, while more particularly hating it as, in his opinion, a dangerous enemy to all social progress. For to him what people called their intuitions, whether theoretic or practical, were merely the time-honoured prejudices in which they had been brought up, and the contradictory of which they could not conceive. Comte similarly interpreted the metaphysical stage of thought as the erection into immutable principles of certain abstract ideas whose value—if they had any—was merely relative and provisional. Mill, with his knowledge of history, might have remembered that past thought, beginning with Plato, shows no such connection between intuitionism and immobility or reaction, while such experientialists as Hobbes and Hume have been political Tories. But in his own time the à priori philosophy went hand in hand with conservatism in Church and State, so he set himself to explode it in his System of Logic (1843).
Mill's Logic, the most important English contribution to philosophy since Hume, is based on Hume's theory of knowledge, amended and supplemented by some German and French ideas. It is conceded to Kant that mathematical truths are synthetic, not analytic. It is not contained in the idea of two and
two that they make four, nor in the idea of two straight lines that they cannot enclose a space. Such propositions are real additions to our knowledge; but it is only experience that justifies us in accepting them. What constitutes their peculiar certainty is that they can be verified by trial on imagined numbers and lines, without reference to external objects. But by what right we generalise from mental experience to all experience Mill does not explain. Hume's analysis of causation into antecedence and sequence of phenomena is accepted by Mill as it was accepted by Kant; but the law that every change must have a cause is affirmed, in adhesion to Dr. Thomas Brown (1778-1820), with more distinctness than by Hume. As Laplace put it, the whole present state of the universe is a product of its whole preceding state. But we only know this truth by experience; and we can conceive a state of things where phenomena succeed one another by a different law or without any law at all. Mill himself was ready to believe that causation did not obtain at some very remote point of space; though what difference remoteness could make, except we suppose it to be causal—which would be a reassertion of the law—he does not explain; nor yet what warrant we have for assuming that causation holds through all time, or at any future moment of time.
Next to the law of universal causation inductive science rests on the doctrine of natural kinds. The material universe is known to consist of a number of substances—namely, the chemical elements and their combinations, so constituted that a certain set of characteristic properties are invariably associated with an indefinite number of other properties. Thus, if in a strange country a certain mineral answers the usual
tests for arsenic, we know that a given dose of it will destroy life; and we are equally certain that if the spectroscopic examination of a new star shows the characteristic lines of iron, a metal possessing all the properties of iron as we find it in our mines is present in that distant luminary. According to Mill, we are justified in drawing that sweeping inference on the strength of a single well-authenticated observation, because we know by innumerable observations on terrestrial substances that natural kinds possessing such index qualities do exist, whereas there is not a single instance of a substance possessing those qualities without the rest.
For Mill, as for Hume, reality means states of consciousness and the relations between them. Matter he defines as a permanent possibility of sensation; mind as a permanent possibility of thought and feeling. But the latter definition is admittedly not satisfactory. For a stream of thoughts and feelings which is proved by memory to have the consciousness of itself seems to be something more than a mere stream. All explanations must end in an ultimate inexplicability. God may be conceived as a series of thoughts and feelings prolonged through eternity; and it is a logically defensible hypothesis that the order of nature was designed by such a being, although the amount of suffering endured by living creatures excludes the notion of a Creator at once beneficent and omnipotent. And if the Darwinian theory were established, the case for a designing intelligence would collapse. Personally Mill believed neither in a God nor in a future life.
In morals Mill may be considered the creator of what Henry Sidgwick, in his Methods of Ethics (1874), called Universalistic Hedonism. The English moralists of the
eighteenth century had set up the greatest happiness of the greatest number as the ideal end of action; but they did not hold that each individual could be expected to pursue anything but his own happiness; the object of Bentham (1748-1832) being to make the two coincide. Kant showed that the rule of right excluded any such accommodation, and a crisis in his own life led Mill to adopt the same conclusion. Afterwards he rather confused the issues by distinguishing between higher and lower pleasures, leaving experts to decide which were the pleasures to be preferred. The universalistic standard settles the question summarily by estimating pleasures according to their social utility.