And so we come to the Dissertation, whose full title is On the Form and Principles of the Sensible and Intelligible World. As the title suggests, Kant sets up his discourse as an Antinomy, a dispute between the Dogmatists and the Sceptics, the Rationalists and the Empiricists, the Leibnizeans and the Newtonians. He is going to try to show that this seemingly irresoluble dispute can be dissolved in such a way that the positive claims of each side are secured, and the attacks of each side on the other evaporate.
Just to anticipate where all this is going, so that you do not get lost in the details of the arguments, Kant is going to go through a four stage process in evolving from the Dissertation doctrine to the full-blown Critical position that emerges in the Critique. First, he presents in the Dissertation what he hopes is a balanced compromise between Leibniz and Newton. Then, almost immediately after delivering his inaugural lecture, he recognizes that his defense of the Leibnizean or Metaphysical side is deeply flawed, and he gives it up, embracing instead a radically new position very heavily weighted toward the Empiricism camp. Third, before he can even put this new position in writing, he re-encounters the deeply sceptical arguments of David Hume, arguments that cast doubt even on the Empiricist position to which he has retreated. This encounter, which as he says in a famous line "awakened me from my dogmatic slumbers," drives him to undertake almost a decade of profound, revolutionary philosophical reasoning that results, in 1781, in the formulation and presentation of the entirely new Critical doctrine of the Critique of Pure Reason. [I have to confess that even after sixty years, it gives me a quiet, private thrill to write these words. I have been away from Kant for too long. As Hannah Arendt said to me once, "It is always so much more pleasant to spend time with Kant."]
The problem, as Kant sees it, lies in forming an adequate representation of a world, which is to say a totality of interacting substances [at this point Kant has in mind Leibnizean monads -- he is still very much writing in the philosophical tradition in which he was educated.] The term "representation," or vorstellung, is Kant's most general term for a cognitively significant content of consciousness. It thus plays somewhat the same role in his writings that "idea" plays in Locke's Essay or that "perception" plays in Hume's Treatise. [Vorstellen in German means literally "to set something before [oneself]."] There is, he thinks [or so he says], no problem in forming an intellectual representation of a totality or world of substances, which is all that is needed to get Leibnizean metaphysics going. But it seems to be impossible to form an adequate sensible representation of such a world, of the sort required by Newtonian Physics. [I hope everyone understands that I am simplifying shamelessly in order not to get hopelessly bogged down.]
The source of this difficulty is that space [and time, but Kant is concerned here with space] is infinitely divisible into ever smaller regions, each containing some degree of force or substance. To form an adequate representation would require going through the process of division step by step, and as there would be an infinite number of such steps -- each one a further division of some region of space -- the process would take an infinitude of time and be impossible to complete. Thus, the Leibnizeans always have an unanswerable objection against the Newtonians, namely that the latter are unable to formulate a useable conception of their object of study. The Newtonians in their turn respond that the Leibnizeans cannot provide the content that their intellectual representations require if they are to yield genuine knowledge. [Anticipating a bit, we see here a very early form of the famous tagline from the Critique: "Thoughts without content are empty. Intuitions without concepts are blind." A51=B75]
To resolve this problem, Kant revives and deploys for his own purposes the ancient distinction between appearance and reality. Leibnizean metaphysics, he says, gives us an adequate intellectual representation of the world as it is in itself, of reality. Newtonian physics, in contrast, provides us with knowledge of that world of monads as they appear to us in sensibility [i.e., through sense perception], hence of appearances.. The spatio-temporal organization of material things is not a characteristic of them as they are, objectively and independently of us. Rather, the mind itself imposes on things a certain spatio-temporal form or organization when it is affected by them and forms sense perceptions of them. This spatio-temporal form of sensibility -- or form of sensible intuition -- lie ready in the mind, prior to all experience. It is not abstracted from experience, as Hume and others thought, but instead exists in the mind a priori.
It is time to pause again for some terminological clarifications. As surely all of you know, even those in the third group of -- dare I say it -- Kantian virgins -- the terms a priori and a posteriori appear again and again in Kant's mature writings, along with two other terms, analytic and synthetic. Indeed, the bastard phrase "synthetic a priori" might be considered his ham operator call sign. But as is so often the case, even those who should know better misuse these terms in confusing ways.
a priori and a posteriori are adverbs, and they modify verbs -- usually, the verb "to know," but also, as in the last sentence two paragraphs ago, the verb "to exist." As Kant uses them, they mean roughly "prior to, or independently of, experience" and "posterior to, or dependent on, experience." A proper Kantian use of the terms would be, for example, "We know the truth of the Causal Maxim a priori, but we only know the truth of particular judgments about the characteristics of the material world a posteriori."
analytic and synthetic are adjectives. They modify nouns, principally the nouns judgment and proposition. A proposition is said to be analytic if [to put it as simply as possible] the concept of the predicate does not add anything to the concept of the subject. It is said to be synthetic if it does add something not contained in the subject concept. Thus "Triangles have three angles" is analytic because "having three angles" is contained in the concept of "being a triangle." "Horses are used as beasts of burden" is synthetic. And so forth. Analytic propositions are also called tautologies, or sometimes miserable tautologies [logicians can be very judgmental.]
Everyone [in Kant's day -- never mind about now] thought it was obvious that the truth of an analytic proposition can be known a priori, since all one need do is unpack what is contained in the subject concept of the proposition, without reference to any experience. So one would say that analytic propositions are knowable a priori. Sometimes, for compactness, the "knowable" was elided, and one simply says that analytic propositions are a priori, but in that statement, a priori is NOT being used as an adjective. It is still an adverb, modifying the missing verb "to know." Until Kant came along, it was widely taken as obvious that synthetic propositions are only knowable a posteriori, that is by appeal to observation or experience. So one might say, compactly, that synthetic propositions are [knowable] a posteriori. But it is NEVER correct to say that there are synthetic a posteriori propositions, as though that were some classification of types of propositions. Kant himself never writes that way, although that fact is obscured by the translations. He always writes "synthetische urteile a priori," not "synthetische a prior urtiele."
Whew. is that all clear? I hope so. Now, back to our regular programming.