Leibnitz regarded the monads as possessing ideas of various grades of clearness and dis tinctness, and believed that matter was made up of those with the vaguest ideas. Because he considered matter to be of the nature of mind, Leibnitz is called an idealist, and is classed to gether with Berkeley, whom we shall next con sider. By observing the vast distance that separates the philosophies of these two men, it will be possible to see how little content inheres in this term, which, with its contradictory real ism, has been singled out by a certain American philosophical school as the index of a grand dichotomy of all philosophical systems.
Berkeley belongs to the British empiridstic tradition. His immediate philosophical ances tor is Locke. Unlike Locke, however, Berkeley saw that no object not directly given can fur nish a test of empirical reality, nor an aid in its explanation. Accordingly, his world con sists of selves and their ideas or sense-data. This does not mean that he rejected natural sci ence, but that he insisted that all its proposi tions were capable of expression in terms of ideas. Such ideas as are not immediately given i to any person he considered to reside in the mind of God, one of whose functions it be comes, to put it crudely, to watch things when nobody is looking and to see that they do not vanish away. However, it will be noticed that an idea in the mind of God which is not ex perienced by us is as inert, remote and useless from an explanatory point of view as a bit of matter. Furthermore, the self apart from its ideas does not appear to play any great part in knowledge. Given an nothing more seems to be added by the adjunction of the self. For these reasons, the next successor to the British tradition, David Hume, rejected both the Berkeleyan matter — thinking God and the soul as a specific entity, and interpreted the world purely and simply as an aggregate of sense-data.
We thus see the contrast between the nat ural-scientific and the Humian view of the uni verse; for the naive scientist, a bit of experience is really an aggregate of atoms in motion, whereas for Hume an atom in motion would have to be interpreted in terms of bits of ex perience. Unfortunately, Hume possessed neither the scientific knowledge nor the logical mechanism to carry out this process in any but the crudest and most schematic way, and hip philosophy of time and causality is in detail as bare and inadequate and unsatisfac tory as any yet devised. Recently, however, Bertrand Russell, who is essentially a Humian in spirit, though he adopts the independent nature of the soul as at any rate a plausible hypothesis, has developed a treatment of these subjects, and of many other allied ones, which is at once scientific and at bottom after the manner of Hume. Matter, for instance, is treated as the system (Hume would have erred by saying "the sum))) of its appearances; an atom or electron becomes a class of sense-data or a relation between them, or something of this general nature. The scientific analysis in terms of atoms angl electrons is recognized as valid, but as based on a deeper analysis into the experiences out of which atoms and elec trons are artefacts.
This recrudescence of British empiricism, however valid its opinions and valuable its re sults may be, is off the main stream of philo sophical development during the latter part of the 18th century and the entire 19th. This
main stream has its source in Kant, who, to continue the metaphor, marks the junction of the currents of British and of Continental thought. What is most distinctive in the thought of Kant is his definite and final occu pation of the standpoint of epistemology, as the true ground for the determination of the prob lems of metaphysics. Now in so doing, Kant is making thought the measure of reality, and this seems to be only repeating the judgment of Spinoza. BM there is a great difference. Kant declines to accept Spinoza's doctrine of thought and reality. The real is more than the con tent of thought. In fact Kant returns to the ancient intuition of thought as formal, and the real as in some sense its correspondent. This was also the tradition of Locke and his school, from which Hume departed, as we have seen, with a result that is often called scepticism. Now the history of Kant's thought shows that, while he clung to the belief in the mere formal character of his tendency was also strongly in the direction of scepticism. More over it was on account of his failure to com pletely achieve what he calls his Copernican revolution, and which was in fact a reaction toward a constitutive doctrine of thought, that he was never able, during the whole of his crit ical period,. to reach a satisfactory conception of the relation of thought to reality. Had Kant completely achieved the mental revolution he proposed, the result would have been, that in epistemology he would have asserted the doc trine of Spinoza, the identity of the real with the content of thought. The knowable world would thus have been identical with the real world and Kant would have escaped the dual ism between knowledge and reality into which he actually fell. Kant also denies the univer sality of thought; at least in the ontological sense. The thought that functions epistemo logically is my human relative thought which can only pronounce judgments that are sub jectively valid for me, but have no ontological value for reality. The Kantian metaphysics is a corollary from his epistemology. What Kant calls critical idealism is first an epistemology, secondly a metaphysic. As an epistemology it teaches that my thought is constitutive for me; that is, that its content is valid for my sub jective connation. It gives me a world, in other words, in which I can work out the prac tical issues of my life, but it does not give me the world of real things in themselves with respect to which my attitude must be one of renunciation. As a metaphysic critical idealism simply carries its program out in the field of ontology. The presumption of the i what is thought with the real cannot be carried out objectively. Kant's metaphysics is there fore necessarily negative. Thought is able to complete itself ontologically, it is true, hut the ideals it reaches have no other than subjective value. Their hypothetical content can never be identified with the real, and the Kantian is per force obliged to represent the whole ontological region as an indeterminate X and to look for the satisfaction of his wants to extra-metaphysi cal forces. These he finds in the domain of ethics.