From this grand synthesis, however, a single element was omitted; and, like the uninvited guest of fairy tradition, it proved strong enough singly to destroy what had been constructed by the united efforts of all the rest. This was the sceptical principle, the critical analysis of ideas, first exercised by Protagoras, made a new starting-point by Socrates, carried to perfection by Plato, supplementing experience with Aristotle, and finally proclaimed in its purity as the sole function of philosophy by an entire school of Greek thought.
Notwithstanding the sterility commonly associated with mere negation, it was this which, of all the later Greek schools, possessed the greatest powers of growth. Besides passing through more than one stage of development on its own account, Scepticism imposed serious modifications on Stoicism, gave birth to Eclecticism, and contributed to the establishment of Neo-Platonism. The explanation is not far to seek. The more highly organised a system is, the more resistance does it offer to change, the more does its transmission tend to assume a rigidly scholastic form. To such dogmatism the Sceptics were, on principle, opposed; and by keeping the problems of philosophy open, they facilitated the task of all who had a new solution to offer; while mind and its activities being, to some extent, safe from the universal doubt, the sceptical principle spontaneously threw back thought on a subjective instead of an objective synthesis of knowledge—in other words, on that psychological idealism the pregnancy and comprehensiveness of which are every day becoming more clearly recognised. And we shall now see how the same fertilising power of criticism has been manifested in modern times as well.
The sceptical philosophy, already advocated in the Middle Ages by John of Salisbury, was, like every other form of ancient thought, revived at the Renaissance, but only under the very superficial form which infers from the co-existence of many divergent opinions that none of them can be true. Even so, however, it led Montaigne to sounder notions of toleration and humanity than were entertained by any of his contemporaries. With Bacon, and still more with Descartes, it also appears as the necessary preparation for a remodelling of all belief; but the great dogmatic systems still exercised such a potent influence on both those thinkers that their professed demand for a new method merely leads up to an altered statement of the old unproved assumptions.
Meanwhile the old principle of universal doubt could no longer be maintained in presence of the certainties already won by modern science. Man, in the time of Newton, had, as Pope tersely puts it, ‘too much knowledge for the sceptic side.’ The problem was not how to establish the reality, but how to ascertain the origin and possible extent of that knowledge. The first to perceive this, the first to evolve criticism out of scepticism, and therefore the real founder of modern philosophy, was Locke. Nevertheless, even with him, the advantage of studying the more recent in close connexion with the earlier developments of thought does not cease; it only enters on a new phase. If he cannot, like his predecessors, be directly affiliated to one or more of the Greek schools, his position can be illustrated by a parallel derived from the history of those schools. What Arcesilaus and Carneades had been to Socrates and his successors, that Locke was, in a large measure, to Bacon and the Cartesians. He went back to the initial doubt which with them had been overborne by the dogmatic reaction, and insisted on making it a reality. The spirit of the Apologia is absent from Plato’s later dialogues, only to reappear with even more than its original power in the teaching of the New Academy. And, in like manner, Descartes’ introspective method, with its demand for clear ideas, becomes, in the Essay concerning Human Understanding, an irresistible solvent for the psychologyy and physics of its first propounder. The doctrine of innate ideas, the doctrine that extension is the essence of matter, the doctrine that thought is the essence of mind, the more general doctrine, held also by Bacon, that things have a discoverable essence whence all their properties may be deduced by a process analogous to mathematical reasoning,—all collapsed when brought to the test of definite and concrete experience.
We have here, indeed, something comparable not only to the scepticism of the New Academy, but also to the Aristotelian criticism of Plato’s metaphysics; and, at first sight, it might seem as if the Peripatetic philosophy was destined once more to regain the position taken from it by the resuscitation of its ancient foe. But Locke was not inclined to substitute one form of scholasticism for another. By applying the analytical method of Atomism to knowledge itself, he created a weapon equally fatal to the two competing systems. Under his dissection, the concrete individual substance of the one vanished no less completely than the universal ideas of the other. Nothing remained but a bundle of qualities held together by a subjective bond.
Similarly, in political science, the analytical method of assuming civil government to result from a concurrence of individual wills, which with Hobbes had served only to destroy ecclesiastical authority, while leaving intact and even strengthening the authority of secular rulers, was reinterpreted by Locke as a negation of all absolutism whatever.
It is interesting to observe how, here also, the positive science of the age had a large share in determining its philosophic character. Founded on the discovery of the earth’s true shape, Aristotle’s metaphysics had been overthrown by the discovery of the earth’s motion. And now the claims of Cartesianism to have furnished an exact knowledge of matter and a definition of it whence all the facts of observation could be deduced à priori, were summarily refuted by the discovery of universal gravitation. The Cartesians complained that Newton was bringing back the occult qualities of the Schoolmen; but the tendency of bodies to move towards one another proved as certain as it was inexplicably mysterious. For a time, the study of causes was superseded by the study of laws; and the new method of physical science moved in perfect harmony with the phenomenism of Locke. One most important consequence of this revolution was to place the new Critical philosophy on a footing quite different from that occupied by the ancient sceptics. Both restricted certain knowledge to our own states of consciousness; but it now appeared that this might be done without impeaching the value of accepted scientific conclusions, which was more than the Academic philosophy would have admitted. In other words, granting that we were limited to phenomena, it was shown that science consisted in ascertaining the relations of these phenomena to one another, instead of to a problematic reality lying behind them; while, that such relations existed and were, in fact, part of the phenomena themselves, was what no sceptic could easily deny.
Nevertheless, in each case, subjective idealism had the effect of concentrating speculation, properly so called, on ethical and practical interests. Locke struck the keynote of eighteenth century philosophy when he pronounced morality to be ‘the proper science and business of mankind in general.’[574] And no sooner had morality come to the front than the significance of ancient thought again made itself apparent. Whether through conscious imitation, or because the same causes brought about the same effects, ethical enquiries moved along the lines originally laid down in the schools of Athens. When rules of conduct were not directly referred to a divine revelation, they were based either on a supposed law of Nature, or on the necessities of human happiness, or on some combination of the two. Nothing is more characteristic of the eighteenth century than its worship of Nature. Even the theology of the age is deeply coloured by it; and with the majority of those who rejected theology it became a new religion. But this sentiment is demonstrably of Greek origin, and found its most elaborate, though not its most absolute, expression in Stoicism. The Stoics had inherited it from the Cynics, who held the faith in greater purity; and these, again, so far as we can judge, from a certain Sophistic school, some fragments of whose teaching have been preserved by Xenophon and Plato; while the first who gave wide currency to this famous abstraction was, in all probability, Heracleitus. To the Stoics, however, is due that intimate association of naturalism with teleology which meets us again in the philosophy of the last century, and even now wherever the doctrine of evolution has not been thoroughly accepted. It was assumed, in the teeth of all evidence, that Nature bears the marks of a uniformly beneficent design, that evil is exclusively of human origin, and that even human nature is essentially good when unspoiled by artificial restrictions.
Yet if teleology was, in some respects, a falling-off from the rigid mechanicism first taught by the pre-Socratic schools and then again by the Cartesian school, in at least one respect it marked a comparative progress. For the first attempts made both by ancient and modern philosophy to explain vital phenomena on purely mechanical principles were altogether premature; and the immense extension of biological knowledge which took place subsequently to both, could not but bring about an irresistible movement in the opposite direction. The first to revive teleology was Leibniz, who furnished a transition from the seventeenth to the eighteenth century by his monadology. In this, Atomism is combined with Aristotelian ideas, just as it had previously been combined with Platonic ideas by Descartes. The movement of the atoms is explained by their aspiration after a more perfect state instead of by mechanical pressure. But while Leibniz still relies on the ontological argument of Descartes to prove the existence of God, this was soon abandoned, along with the cosmological argument, for the argument from design, which was also that used by the Stoics; while in ethics the fitness of things was substituted for the more mechanical law of self-preservation, as the rule of conduct; and the subjection of all impulse to reason was replaced by the milder principle of a control exercised by the benevolent over the malevolent instincts. This was a very distinct departure from the Stoic method, yet those who made it were more faithful to teleology than Stoicism had been; for to condemn human feeling altogether was implicitly to condemn the work of Nature or of God.
The other great ethical method of the eighteenth century, its hedonism, was closely connected with the sceptical movement in speculative philosophy, and, like that, received an entirely new significance by becoming associated with the idea of law. Those who isolate man from the universe are necessarily led to seek in his interests as such the sole regulator of his actions, and their sole sanction in the opinion of his fellows. Protagoras went already so far, notwithstanding his unwillingness to recognise pleasure as the supreme end; and in the system of his true successor, Aristippus, the most extreme hedonism goes hand in hand with the most extreme idealism; while with Epicurus, again, both are tempered by the influence of naturalism, imposing on him its conceptions of objective law alike in science and in practice. Still his system leaned heavily to the side of self-gratification pure and simple; and it was reserved for modern thought to establish a complete equilibrium between the two competing tendencies of Greek ethics. This has been effected in Utilitarianism; and those critics are entirely mistaken who, like M. Guyau, regard that system as a mere reproduction of Epicureanism. It might with full as much reason be called a modern version of Stoicism. The idea of humanity is essentially Stoic; to work for the good of humanity was a Stoic precept; and to sacrifice one’s own pleasure for that higher good is a virtue which would have satisfied the most rigorous demands of a Cleanthes, an Epictêtus, or an Aurelius.