section_path: Philosophy/Kant's critical project
section_name: Kant's critical project
paragraph_text: Kant's critical project
  
  Kant's 1781 (revised 1787) book the Critique of Pure Reason has often been cited as the most significant volume of metaphysics and epistemology in modern philosophy. In the first Critique, and later on in other works as well, Kant frames the "general" and "real problem of pure reason" in terms of the following question: "How are synthetic judgments a priori possible?" To understand this claim, it is necessary to define some terms. First, Kant makes a distinction between two sources of knowledge:
  
  Second, he makes a distinction in terms of the form of knowledge:
  
  An analytic proposition is true by nature of strictly conceptual relations. All analytic propositions are a priori (it is analytically true that no analytic proposition could be a posteriori). By contrast, a synthetic proposition is one the content of which includes something new. The truth or falsehood of a synthetic statement depends upon something more than what is contained in its concepts. The most obvious form of synthetic proposition is a simple empirical observation.
  
  Philosophers such as David Hume believed that these were the only possible kinds of human reason and investigation, which he called "relations of ideas" and "matters of fact". Establishing the synthetic a priori as a third mode of knowledge would allow Kant to push back against Hume's skepticism about such matters as causation and metaphysical knowledge more generally. This is because, unlike a posteriori cognition, a priori cognition has "true or strict... universality" and includes a claim of "necessity". Kant himself regards it as uncontroversial that we do have synthetic a priori knowledge — most obviously, that of mathematics. That 7 + 5 = 12, he claims, is a result not contained in the concepts of seven, five, and the addition operation. Yet, although he considers the possibility of such knowledge to be obvious, Kant nevertheless assumes the burden of providing a philosophical proof that we have a priori knowledge in mathematics, the natural sciences, and metaphysics. It is the twofold aim of the Critique both to prove and to explain the possibility of this knowledge. Kant says "There are two stems of human cognition, which may perhaps arise from a common but to us unknown root, namely sensibility and understanding, through the first of which objects are given to us, but through the second of which they are thought."
  
  Kant's term for the object of sensibility is intuition, and his term for the object of the understanding is concept. In general terms, the former is a non-discursive representation of a particular object, and the latter is a discursive (or mediate) representation of a general type of object. The conditions of possible experience require both intuitions and concepts, that is, the affection of the receptive sensibility and the actively synthesizing power of the understanding. Thus the statement: "Thoughts without content are empty, intuitions without concepts are blind." Kant's basic strategy in the first half of his book will be to argue that some intuitions and concepts are pure — that is, are contributed entirely by the mind, independent of anything empirical. Knowledge generated on this basis, under certain conditions, can be synthetic a priori. This insight is known as Kant's "Copernican revolution", because, just as Copernicus advanced astronomy by way of a radical shift in perspective, so Kant here claims do the same for metaphysics. The second half of the Critique is the explicitly critical part. In this "transcendental dialectic", Kant argues that many of the claims of traditional rationalist metaphysics violate the criteria he claims to establish in the first, "constructive" part of his book. As Kant observes, "human reason, without being moved by the mere vanity of knowing it all, inexorably pushes on, driven by its own need to such questions that cannot be answered by any experiential use of reason". It is the project of "the critique of pure reason" to establish the limits as to just how far reason may legitimately so proceed.