[This excerpt is from Chapter 2 of Explaining Postmodernism: Skepticism and Socialism from Rousseau to Foucault]
Kant’s essential argument
Kant began by identifying a premise common to both empiricists and rationalists. They had assumed that knowledge must be objective. That is, they took for granted that the object of knowledge sets the terms and that therefore it was up to the subject to identify the object on the object’s terms. In other words, the empiricists and the rationalists were realists: they believed that reality is what it is independently of consciousness, and that the purpose of consciousness is to come to an awareness of reality as it is. In Kant’s terms, they assumed that the subject is to conform to object. Kant then noted that the realist/objectivist assumption had led repeatedly to failure, and—more strikingly—that it must necessarily lead to failure.
To demonstrate this, Kant proposed a dilemma for all analyses of knowledge. The first premise of the dilemma is given at the beginning of the Transcendental Deduction. Here Kant states that knowledge of objects can come to be in only one of two ways.
There are only two possible ways in which synthetic representations [i.e., what one experiences] and their objects can establish connection, obtain necessary relation to one another, and, as it were, meet one another. Either the object alone must make the representation possible, or the representation alone must make the object possible.
The terms of the dilemma are crucial, particularly for the first alternative. If we say that “the object alone must make the representation possible,” then we imply that the subject must have nothing to do with the process. The implication is that the subject can have no identity of its own, that the mind must not be anything in particular, that consciousness must be, to borrow a phrase, a purely “diaphanous” medium on which or through which reality writes itself. In other words, Kant assumed—as had most thinkers before him—that objectivity presupposes naïve realism’s metaphysics of an identity-less subject.
But clearly that metaphysics of mind is hopeless. This was Kant’s next premise. The knowing subject is something: its processes are causal and definite, and they shape the subject’s awareness. In Kant’s words, when we experience “we always remain involved in conditions,” conditions that make our experiences a “finite synthesis.”
This is why naïve realism has been an impossible project. The knowing subject is not a blank, identity-less tablet, so it cannot be that the object alone makes knowledge possible. Given its finite identity, the knowing subject is implicated in producing its experiences, and from the limited and conditioned experiences that are produced the subject cannot read off what is really real.
Thus we arrive at the second alternative, the one that Kant proposed as being true—namely that the representation makes the object possible. And thus we have part of the motivation for Kant’s “Copernican” revolution in philosophy, announced in the Second Preface. Given that the knowing subject has an identity, we must abandon the traditional assumption that the subject conforms to the object. Accordingly, the converse must be true: the object must conform to the subject, and only if we make that assumption—i.e., only if we abandon objectivity for subjectivity—can we can make sense of empirical knowledge.
The second part of Kant’s motivation was attempting to make sense of necessary and universal concepts and propositions. Neither the rationalists nor the empiricists had found a way to derive them from experience. Kant again faulted their assumption of realism and objectivism. Those assumptions made the project impossible. “In the former case [i.e., the object alone making the representation possible], this relation is only empirical, and the representation is never possible a priori.” Or putting the point in language Kant had learned from Hume, passive experience will never reveal what must be, for such experience “teaches us that a thing is so and so, but not that it cannot be otherwise.”
So again we must infer that the converse is true: Necessity and universality must be functions of the knowing subject, not items impressed upon subjects by objects. If we assume that our identity as knowing subjects is implicated in constructing our experiences, then we can assume that our identity will generate certain necessary and universal features of our experiences. Accordingly we have Kant’s central project in the first Critique of tracking down fourteen such constructive functions of the subject: space and time as two forms of sensibility, and the twelve categories. As a result of the operations of those constructive functions, we can find necessary and universal features within our experiential world—because we have put them there.
Now for the payoffs and trade-offs. The first payoff is that the phenomenal world of experience now has necessary and universal features built into it, so we get a nice, orderly world for science to explore. Science is rescued from the unintended skepticism that the empiricists and rationalists had reached, and its aspiration to discover necessary and universal truths is made possible.
But there is also the Kantian trade-off. The objects that science explores exist “only in our brain,” so we can never come to know the world outside it. Since the phenomenal world’s necessary and universal features are a function of our subjective activities, any necessary and universal features that science discovers in the phenomenal world have application only in the phenomenal world. Science must work with experience and reason, and on Kantian grounds this means that science is cut off from reality itself.
[E]verything intuited in space or time, and therefore all objects of experience possible to us, are nothing but appearances, that is, mere representations, which in the manner in which they are represented, as extended beings, or as series of alterations, have no independent existence outside our thoughts.
As for what has independent existence outside our thoughts, nobody knows or can know.
From Kant’s perspective, that is a trade-off he was happy to make, for science’s loss is religion’s gain. Kant’s argument, if successful, means that “all objections to morality and religion will be forever silenced, and this in Socratic fashion, namely, by the clearest proof of the ignorance of the objectors.” Reason and science are now limited to playing with phenomena, leaving the noumenal realm untouched and untouchable. Having denied knowledge, room was made for faith. For who can say what is or is not out there in the real world?
 Kant 1781, Bxvi.
 Kant 1781, A92/B125.
 Kelley 1986, 22-24.
 Kant 1781, A483/B511.
 Kant 1781, Bxvi-Bxvii.
 Kant 1781, A92/B125.
 Kant 1781, B3.
 Kant 1781, Bxvii-Bxviii; A125-A126.
 Kant 1781, A484/B512.
 Kant 1781, B519/A491.
 Kant 1781, Bxxxi.
[This is an excerpt from Stephen Hicks’s Explaining Postmodernism: Skepticism and Socialism from Rousseau to Foucault (Scholargy Publishing, 2004, 2011). The full book is available in hardcover or e-book at Amazon.com. See also the Explaining Postmodernism page.]