The Inaugural Dissertation of 1770
Although a wide range of philosophical issues make an appearance in the Inaugural Dissertation, one principal focus of Kant's attention is a half century old controversy about the nature of space. Leibniz and Isaac Newton, both of whom could lay claim to having invented the Calculus [there were giants in the earth in those days, as the Good Book says], took opposed positions on the question whether space is independent of the objects in it. Leibniz maintained that the only real things are unitary, immaterial substances, which he called monads. Space, he argued, is simply the totality of the external relations among the infinity of monads [among which, by the way, are human minds.] Speaking mathematically, one can conceive of monads in Leibniz's metaphysical system as dimensionless points, having only location. Each monad was thought by Leibniz to embody a certain quantum of force ["living force," or, as Kant expressed it, "lebendige kraft."] Thus, the entire universe is a plenum of point sources of force or density or impenetrability. It follows from Leibniz's account that there cannot be empty space, space entirely devoid of substances. Descartes, you will recall, argued that the defining characteristic of material substance is extension, which also implies the impossibility of a void [which is to say, extension devoid of material substance. Descartes invented what we call Cartesian Geometry in support of his view. Those guys really were something.]
Newton took the opposed position, that space is prior to and independent of what fills it. He did not offer a philosophical account of the nature of space, as Leibniz had done, simply describing it somewhat obscurely as "God's sensorium." Newton's position was dictated by what he considered requisite for his physical theories, and in one passage in the Principia, he famously said that he "eschewed hypotheses," which is to say fruitless metaphysical speculations.
The debate between what came to be described as The Metaphysical Philosophy and the Physical Philosophy found public expression in a series of five brilliant epistolary exchanges in 1715 and 1716 between Leibniz himself and Samuel Clarke, a follower of Newton. The letters were published in both French and English and served as the best known contemporary statement of Leibniz's views. [The more important Monadology had not been published at the time.]
The dispute can fairly be described as a stand-off. Leibniz's elegant and carefully worked out metaphysics of monads was vastly superior to Newton's offhand description of space as God's sensorium [time, by the way, was pretty much of a poor relation in the debate, although both authors treated it as formulaically on a par with space]. But on one crucial point, Clarke clearly had the better of Leibniz. Leibniz had argued, against the Newtonian position of the absolute existence of space, that if God chose to create the universe three feet to the left of where it was currently positioned, or if He were to cause the entire universe of physical substances to accelerate, this fact would be totally unobservable by us, and hence be as nothing. But Clarke, relying on Newton's laws of motion and their mathematical implications, replied quite correctly that an acceleration or deceleration would in fact produce observable effects within our world, and thus be real.
One final, very small, but elegant point. Leibniz argued that if Newton were right, then God could have chosen to create a mirror image of the universe. But since properties like "to the left of" and "to the right of," or "above" and "below," are simply relations of pre-existing monads, there could not be, as he put it, a sufficient reason for God to create the universe in one way rather than another, for an image and its mirror are identical in all the relations of their parts. In a paper written shortly before the Inaugural Dissertation, Kant refuted Leibniz, arguing that there are in nature many pairs of objects which are incongruous [cannot be made to overlap], even though they are identical in all of the relations of their parts. His most famous example is a left hand and a completely similar right hand, which cannot be made congruent [at least not in three dimensional space -- in four dimensional space, one could flip a right hand glove through the fourth dimension and make it congruent with its left hand counterpart, just as in three dimensional space one can flip a triangle oriented one way to make it congruent with a mathematically similar triangle -- all the sides and angles equal -- oriented the other way.]
In the Dissertation, Kant puts forward an ingenious theory that not only resolves the dispute between the Leibnizeans and the Newtonians, but also, at the same time, splits the difference between the rationalist claim that reason is the sole source of reliable knowledge and the empiricist counterclaim that sense perception is the foundation of human knowledge. Viewed in retrospect from the perspective of Kant's fully developed epistemological theories in the First Critique, we can see the position of the Dissertation as a half-way house on Kant's epic journey from the Wolffian metaphysics of his youth to the revolutionary teaching of the Critical Philosophy. Not for nothing is the doctrine of the Dissertation referred to by Kant scholars as 'Semi-Critical." It is useful for us to approach the full-blown teaching of the Critique by way of the doctrines of the Dissertation because this will enable us to pinpoint just exactly what the problem was that forced Kant to move beyond the comfortable middle position achieved in the Dissertation. [Just to whet your appetite, the problem, in word, was Hume.]
And now, a word about terminology. [This one's for Chris.] There was in Kant's day a familiar and non-controversial pair of distinctions between the ways in which the mind can stand in relation to an object. These are distinctions with a long and distinguished pedigree, traceable back at least to the disputations of the scholastic philosophers of the twelfth and thirteenth centuries. The mind can stand in immediate relation to an object, or in a mediate or indirect relation to an object. And this relation can be passive or active.
When I perceive an object with my senses -- when I see it, hear it, smell it, taste it, or feel it -- my mind [these folks all agreed] is in direct or immediate relation to a single individual thing. I see this horse, I feel this tree with my hand, I hear that piano. Furthermore, the mind's relation to the object is passive, not active. It does not create the object. It waits upon the object to affect the senses, in whatever manner that occurs. When God brings an object into existence by creating it, His relation to it also is immediate and direct, but in His case the relation is active, not passive. The object does not affect Him. He creates it.
The immediate relation of the mind to an object was called intuition. In the case of human beings, this intuition is sensuous and passive. Thus, sense perception is passive or sensuous intuition. In the case of God [and no one else], His intuition is intellectual, or active, or creative. If one wishes, one can put this last point in the subjunctive without altering the meanings of the terms: If there were a god, his intuition would be intellectual.
When the mind apprehends an object by means of concepts, its relation to the object is indirect, mediate. It is mediated by a general or universal notion, under which it subsumes the individual that the mind is apprehending. So, I invoke the general concept "horse," which of course applies to many objects, and subsume my perception of an object before me under that general concept, as when I form the judgment, "This is a horse." Conception is always active, not passive, but it is not always creative. When I form a general concept of a house, and then act so as to build the house -- when, in short, I make my concept actual, or actualize it -- then my conception is both active and creative. But when I bring concepts to bear on my perceptions and form judgments of the type or kind or species of thing I am perceiving, my conception, while still active, is not creative.
[There is an old dispute about whether God's intellect is intuitive or conceptual. Aristotle, in one of my favorite passages from ancient philosophy, argues that the Prime Mover apprehends universals, not particulars, suggesting, by analogy with the lord of an estate, that there are certain things it is better for a gentleman not to know. Christianity, on the other hand, is quite clear that God numbers the hairs on my head and the sparrows in the air. "His eye is on the sparrow," in the words of the hymn.]