Concluding thoughts on the Postulates of Empirical Thought
Kant’s “General Note” at the end of the “Postulates of Empirical Thought” represents his attempt to show what he thinks he has accomplished in The System of the Principles of the Pure Understanding. It may be recalled from earlier discussions of this section that the general objective of these sections (including the Principles, the Analogies, and the Postulates) was to bridge a gap between the pure principles of the understanding and our experience. Specifically, the question Kant is trying to answer is how those pure principles of the understanding can be applied to our sensory intuitions to produce “experience” (which involves both our understanding and sensory experience) and empirical knowledge. The General Note rounds out the picture of what Kant thinks he has accomplished.
Conveniently, he summarizes the results himself as follows:
The final outcome of this whole section is therefore this: all principles of the pure understanding are nothing more than principles a priori of the possibility of experience, and to experience alone do all a priori synthetic propositions relate–indeed, their possibility itself rests entirely on this relation.
B294
It will be the goal of what follows to unpack these few lines in order to better understand their significance and gain a better general understanding of how the pure principles of the understanding relate to our sensory intuitions to give us our experience of the world
Contents:
The Possibility of Experience
Kant begins this section by reintroducing his discussion of possibility. It may be recalled that Kant had originally provided a definition of the concept at the very beginning of the section on the Postulates as follows:
That which agrees with the formal conditions of experience, that is, with the conditions of intuition and concepts is possible.”
B265
It may be seen from the definition alone that “possibility,” as Kant intends us to understand, is framed within the broader constraints of what it is possible for us to experience. Those constraints are provided by “the conditions of intuitions and concepts” in other words, space and time on the one hand and the categories of our understanding as possible judgments on the other.
Because the other two postulates have not yet been provided, they will be given here as follows:
2. That which is bound up with the material conditions of experience, that is, with sensation, is actual.
3. That which in its connection with the actual is determined in accordance with universal conditions of experience, is (that is, exists as) necessary.
B266
It may be seen that in each case possibility, actuality, and necessity are all defined in terms of experience: what is possible are necessary or actually before us are all thought of as being definable in terms of the conditions that constrain experience in general. The entire category of modality, in other words, is itself defined by the matrix of forms of thought and intuition that structures our experience of the world. It is in this sense that “all principles of the pure understanding are nothing more than principles a priori of the possibility of experience” as Kant puts it in his summary.
The Categories as Pure, General Ideas in Need of Content
But the further point Kant is interested in driving home in this section is that nothing about our experience of reality can be determined from such a priori principles alone; the principles that structure reality are, by themselves, not sufficient to tell us anything about reality itself and do not themselves become part of our experience except by way of sensory intuition. Without the senses, they are merely empty, without content, or in another way of expressing it, pure. One might think of the categories and the pure concepts they provide as the shapes that cut what may be understood and recognized from the dough of our sensory field, but with the following caveat: we have no access to the dough in this analogy except by way of the cookie cutters. Our mental reality is “always already” as it were, shaped by the cutting tools the mind is provided with and it is with these tools that experience, in the broad sense that Kant intends the term can take shape at all.
The categories of relation provide an example. As Kant puts it, (1) apart from the mere concepts there is no way we can understand how something can be understood as a pure subject of determinations (here he responds to skepticism about substance); nor (2) can we understand how because one thing is, another must be (causality and necessity); nor again (3) can we understand how both concepts can be combined to yield the notion of a community of interdependent substances. The three points make up the content of the analogies of experience. But the broader point is that these relations together give us the possibility of understanding the world about us by providing us with a means of connecting pure ideas with our purely sensory experience of the world. Whereas empirical skepticism waged a campaign against the possibility of understanding substantiality, causality, and community on their own terms apart from experience, Kant argues that experience such as we know it (including our ability to understand) it would not be possible without the pure ideas and forms or experience that shape it (recalling the analogy above) within our field of conscious awareness. They provide us, in other words, with a way of understanding the world that is itself incomprehensible apart from our sensory experience.
Synthesis
The fact that these categories give us a way of understanding the world about us is an ideal transition point for discussing the nature of a priori synthesis. It occurs by means of the application of the categories to our sensory intuitions of the world and can be understood in its most basic form as having the structure of a judgment. If the categories alone are considered, we will be in no position to say that, for example, “in all existence there is substance” or that “everything is a quantum” [B289]. And indeed, it would be difficult to make sense of such statements at all apart from the matter of experience. Again, in terms of the analogy above, the shape requires the material of the dough in order that it may become an object of contemplation for us, or as Kant puts it, “in order to exhibit the objective reality of the pure concept of understanding we must always have an intuition” [B288].
Kant emphasizes that synthetic judgments involve “going out beyond a given concept.” Perhaps the clearest way to understand this point is to recall the notion of an analytic proposition. All those propositions whose truth can be considered a matter of pure logical entailment, such as that “A triangle is a three-sided figure,” can be considered true apart from experience. Even more, they can be considered irrelevant to experience, or as Kant puts it in terms that echo the same point, “the possibility of a thing cannot be determined from the category alone” [B288] or again, “no one…has ever yet succeeded in in proving a synthetic proposition merely from pure concepts of the understanding” [B289]. This delineation of analytic propositions helps to see where the domain of synthetic ones lies.
These are propositions such as that “everything that exists has a cause” where the concept of existence does not necessarily entail that of being caused. After all, there is nothing logically impossible about the notion of an uncaused cause as there might be in the case of a square circle–where neither concept can imply the other without contradiction. If such propositions are true, they must be true in virtue of something other than pure logical entailment. That something, Kant says, is experience. This may seem puzzling because a priori propositions ought to be true by virtue of pure ideas. It seems we must have a conflict between experience and pure ideas insofar as which does the work of truth certification. It appears that the notion of an a priori synthesis must involve a contradiction in terms.
The Categories as Forms our Thought Can Take
But the kind of a priori certification Kant has in mind does not come from ideas that float somewhere above us in a Platonic heaven or in a purely logical, quasi-mathematical space where tautological propositions stand as axioms for further deductions, but from the categories of thought, which are the forms our understanding can take. It is by virtue of the fit with experience, or the shape that the raw material of experience takes for us that synthetic propositions are in a sense destined to make sense to us. If we take another of Kant’s examples, “everything which exists contingently has a cause” the basic rationality of the proposition is difficult to question: what might have existed and does exist must have been brought into existence by something else. Even if an uncaused cause is conceivable, the rationality of such statements has a way of compelling our assent. It is such propositions that structure the way we apply our rationality to the sensory experience we have of the world about ourselves.
Conclusion
Let’s return to the original quotation and consider what has been brought to light:
The final outcome of this whole section is therefore this: all principles of the pure understanding are nothing more than principles a priori of the possibility of experience, and to experience alone do all a priori synthetic propositions relate–indeed, their possibility itself rests entirely on this relation.
B294
It should be evident that possibility, experience and synthesis all go hand in hand with our capacity to understand the world about us. The move that Kant makes that his predecessors did not was to take understanding as a fact of our experience. If we consider not the logic of the proposition “2+2=4” but its rationality, the fact that it seems impossible to doubt indicates something about our way of understanding the world.
It tells us something about how we understand the contents of our conscious awareness. Kant’s move was to say that there are certain patterns latent within our rationality that appear in such propositions. They indicate something about the nature of this “way” and of the “how” of our understanding. Kant’s move to counter the skepticism of the empiricists was to see that such rationally evident propositions not only appear in logically true propositions, but also in propositions about the nature of contingent events whose rational force compels our assent.
