[Footnote 14: That is, as a discipline of the faculties,—the chief benefit to be derived from any kind of metaphysical study.]
Locke's reason for repudiating ontology is the alleged impossibility of arriving at truth in that pursuit,—"of finding satisfaction in a quiet and sure possession of truths that most concern us, whilst we let loose our thoughts into the vast ocean of being." [15] Unfortunately, however, as Kant has shown, the results of noölogical inquiry are just as questionable as those of ontology, whilst the topics on which it is employed are of far inferior moment. If, as Locke intimates, we can know nothing of being without first analyzing the understanding, it is equally sure that we can know nothing of the understanding except in union with and in action on being. And excepting his own fundamental position concerning the sensuous origin of our ideas,—to which few, since Kant, will assent,— there is hardly a theorem, in all the writings of this school, of prime and vital significance. The school is tartly, but aptly, characterized by Professor Ferrier: "Would people inquire directly into the laws of thought and of knowledge by merely looking to knowledge or to thought itself, without attending to what is known or what is thought of? Psychology usually goes to work in this abstract fashion; but such a mode of procedure is hopeless,—as hopeless as the analogous instance by which the wits of old were wont to typify any particularly fruitless undertaking,—namely, the operation of milking a he-goat into a sieve. No milk comes, in the first place, and even that the sieve will not retain! There is a loss of nothing twice over. Like the man milking, the inquirer obtains no milk in the first place; and, in the second place, he loses it, like the man holding the sieve…. Our Scottish philosophy, in particular, has presented a spectacle of this description. Reid obtained no result, owing to the abstract nature of his inquiry, and the nothingness of his system has escaped through all the sieves of his successors." [16]
[Footnote 15: Essay, Book I. Chap. 1, Sect. 7.]
[Footnote 16: Institutes of Metaphysic, p. 301.]
Leibnitz's metaphysical speculations are scattered through a wide variety of writings, many of which are letters to his contemporaries. These Professor Erdmann has incorporated in his edition of the Philosophical Works. Beside these we may mention, as particularly deserving of notice, the "Meditationes de Cognitione, Veritate et Ideis", the "Systeme Nouveau de la Nature", "De Primæ Philosophiæ Emendatione et de Notione Substantiæ", "Reflexions sur l'Essai de l'Entendement humain", "De Rerum Originatione Radicali", "De ipsa Natura", "Considerations sur la Doctrine d'un Esprit universel", "Nouveaux Essais sur l'Entendement humain", "Considerations sur le Principe de Vie". To these we must add the "Théodicée" (though more theological than metaphysical) and the "Monadologie", the most compact philosophical treatise of modern time. It is worthy of note, that, writing in the desultory, fragmentary, and accidental way he did, he not only wrote with unexampled clearness on matters the most abstruse, but never, that we are aware, in all the variety of his communications, extending over so many years, contradicted himself. No philosopher is more intelligible, none more consequent.
In philosophy, Leibnitz was a Realist. We use that term in the modern, not in the scholastic sense. In the scholastic sense, as we have seen, he was not a Realist, but, from childhood up, a Nominalist. But the Realism of the schools has less affinity with the Realism than with the Idealism of the present day.
His opinions must be studied in connection with those of his contemporaries.
Des Cartes, Spinoza, Locke, and Leibnitz, the four most distinguished philosophers of the seventeenth century, represent four widely different and cardinal tendencies in philosophy: Dualism, Idealism, Sensualism, and Realism.
Des Cartes perceived the incompatibility of the two primary qualities of being, thought and extension, as attributes of one and the same (created) substance. He therefore postulated two (created) substances,—one characterized by thought without extension, the other by extension without thought. These two are so alien and so incongruous, that neither can influence the other, or determine the other, or any way relate with the other, except by direct mediation of Deity. (The doctrine of Occasional Causes.) This is Dualism,— that sharp and rigorous antithesis of mind and matter, which Des Cartes, if he did not originate it, was the first to develop into philosophic significance, and which ever since has been the prevailing ontology of the Western world. So deeply has the thought of that master mind inwrought itself into the very consciousness of humanity!
Spinoza saw, that, if God alone can bring mind and matter together and effect a relation between them, it follows that mind and matter, or their attributes, however contrary, do meet in Deity; and if so, what need of three distinct natures? What need of two substances beside God, as subjects of these attributes? Retain the middle term and drop the extremes and you have the Spinozan doctrine of one (uncreated) substance, combining the attributes of thought and extension. This is Pantheism, or objective idealism, as distinguished from the subjective idealism of Fichte. Strange, that the stigma of atheism should have been affixed to a system whose very starting-point is Deity and whose great characteristic is the ignoration of everything but Deity, insomuch that the pure and devout Novalis pronounced the author a God-drunken man, and Spinozism a surfeit of Deity. [17]