(2) The Metaphysics of Natural Science. — Of course, science as such can have no peculiar metaphysics, for the truth is essentially one— unless we adopt the pragmatist attitude — and cannot be changed into a falsehood merely by looking at it through the spectacles of a particular discipline. Nevertheless, there is a certain conventional metaphysics which may be read between the lines of the majority of scientific textbooks, the habitat of which is the laboratory and the specimen-box. Though this may be traced to the Greeks, it owes its incar nation in its present avatar to Descartes and Locke. Both these writers, who are conven tionally called dualists, since they believe in the essential distinctness of mind and matter, are really rather what one might name ternarists, inasmuch as they posit between the self and its objects a third class of entities, the ideas, by the mediation of which the mind or self is aware of the outer world. Dreams differ from true waking experiences in that the ideas they contain have no realities corresponding to them. Modern science has turned the real universe into a world of movements of material par ticles, or of electric charges, without any in trinsic color or sound, and has relegated these latter qualities to the realm of ideas. The physical correlates of these ideas are, of course, particles or charges in motion. By the media tion of the nervous system these particles or charges and their movements are supposed to produce certain alterations in the brain — Des cartes considered that they were in the pineal body, while the advance of modern science has placed them in the cerebral cortex — which have as invariable concomitants certain ideas or ideational processes. It is these that form the sole direct object of human inspection.
This theory is perfectly successful in ex plaining error, but remarkably inadequate in accounting for anything else — any knowledge, that is, which is not a mere accidental blunder ing belief. The situation is quite analogous to that of a man gazing at the cover of a book and trying to know what is inside. This knot or rib in the cloth may cover an exposition of this or that theory, but if the book is per manently locked up, and is opaque, we can never know this. We consequently find that at the very beginning additions and modifica tions were made in the theory. These, how ever, belong to (3) The Metaphysics of the Technical Modern philosophical tradition may be said to commence with Descartes. Ac cordingly, he is the first man with whom the metaphysical issues of the present day recene the division and treatment with which we are familiar. We have seen that he divided the world into separate realms, apparently of mine and matter, but really of soul, matter and ideas Nevertheless, he saw the difficulties of the problem of error and tried to give it a more adequate solution than that pertaining to the conventional philosophy of natural science. As
the founder of modern mathematics he tried to introduce mathematical criteria of truth metaphysics, and so he starts with the propose tion, °I think, therefore, I am,* the denial of which he regards as self-contradictory in the same sense in which has a rational square root* is self-contradictory. Having thus ob tained the existence of the self, he goes oe to demonstrate that God exists: 'I have an idea of a most perfect Being, and this idea can only come from the Being with the one perfection my idea lacks, that of existence.* Once he got this Being, Descartes asserts that oar knowledge of matter receives its guarantee in the honesty of God. This relieves the difficulty we encountered in the metaphysics of the scien tist, the difficulty of bringing ideas and then objects into relation, but it is not by any meant completely satisfactory. If God is honest, how can we make blunders? By failing to have our ideas clear and distinct, says Descartes. Br how can an honest God permit vague ideas' This involves us in the interminable and fruit less controversies concerning the relative pose:. and goodness of God which were so character istic of the medieval schoolmen at their worst.
Descartes' philosophy thus involves a Dew ex mac/:ilia. His followers, without exceptior laid far more emphasis on this phase of his philosophy than he himself. In the systems of Geulincx and Malebranche, God becomes the agent causing every change in mind and mat ter, who for each change in the one wills thy there shall be a corresponding change in the other. From this Occasionalism it is but a step to the monism of Spinoza, for whom mind ani! matter are but two among an infinite number of aspects of the one reality, God. From an other standpoint, the entire world is the contert of intellection, without the mediation of tbe Cartesian and Lockean *ideas.* Spinoza re tains the logical, mathematical, inteltualistk standards of truth and knowledge which were set up by Descartes, but he has also a mystical. emotionalistic view of the nature of reality. in that he believes that this.is most truly perceived through the Intellectual Love of God.
The Deus ex machitsa survives in the viers of the next great continental philosopher, Leib nitz. Instead of the two substances, mind and matter, of the Cartesian tradition, he supposes an infinity of substances, the monads, aear taking to some extent of a mental nature In place of calling upon God's continual interven tion to keep these experiences in accord with the facts, Leibnitz supposes that at the Creation the Lord foreordained that all these many ex periences should keep time, just as two perfect clocks, wound up and set together, will agree on all subsequent occasions until they run down. It will be seen that the problem of error ap pears in the philosophy of Leibnitz almost in its Cartesian form.