My posts in this thread will be a mish-mash of notes, papers/responses revised for the forum, and new material. My rough plan is simply to cover areas of interest starting with the Preface. I am neither psychotic enough, nor so presumptuous to attempt a comprehensive "summary", but will be sure to touch on many "core" issues, however briefly and unsatisfactorily. Basically, just go read it.
Also, I won't attempt to "situate" the Critique historically, or discuss its relation to empiricism and rationalism. If one were interested in quickly reading key texts from both of those movements, I highly recommend Descartes' Meditations and David Hume's An Enquiry Concerning Human Understanding, which are both much shorter than the Critique. In the mean time, I think it appropriate to try and engage the work of such a thinker as Kant, if only to balance all the rabid scientism and "Nietzscheanism" around here. 
First post: Formal Overview of the Preface
"For in [metaphysics] reason continuously gets stuck...we have to retrace our path countless times, because we find that it does not lead where we want to go, and it is so far from reaching unanimity in the assertions of its adherents that it is rather a battlefield, and indeed one that appears to be especially determined for testing one's powers in mock combat; on this battlefield no combatant has ever gained the least bit of ground, nor has any been able to base any lasting possession on his victory. Hence there is no doubt that up to now the procedure of metaphysics has been a mere groping, and what is the worst, a groping among mere concepts." B xv, Cambridge edition. (bold emphasis added)
Kant begins his 1787 Preface to the Critique of Pure Reason by comparing the fruitful progress of the sciences with the deadlock of metaphysics. Since the objects and areas of investigation of the sciences are fundamentally distinct from metaphysics (the latter being "a wholly isolated speculative cognition of reason that elevates itself entirely above all instruction from experience..."), Kant's comparison concerns the methodology of the sciences and what metaphysics can potentially learn from it.
In particular, Kant calls our attention to the work of Copernicus, whose advances in astronomy were made possible by uprooting and reorienting the fundamental assumptions of the field. Copernicus' progress came not by assuming, as was customary, a static observer around which the heavens revolve, but rather in interrogating the observer to see if, in fact, it was he that was in motion. It is in this sense, of a focal inversion from observed "objects" to the observing "subjects," that Kant's Critique initiates a "Copernican revolution" within philosophy.
The first steps in this transformation of the procedure of metaphysics consist in an examination of the traditional assumptions regarding the role of the observer/inquirer- specifically, the intuition of sensible objects (what is given in perception) and the nature of concept formation. Kant claims that until the Critique it was assumed that our cognition conforms to the objects of sensation [the Cambridge edition translates "erkenntnis" as "cognition", and so I also use it on occasion. However, it can also be translated as "knowing" or knowledge, which I usually find preferable to the very general and technical "cognition"; contemporary readers might interpret the latter as simply "thought" or some minimal mental event or process, which is not what Kant means]. Under this assumption, the faculty of intuition plays only a "passive" role in the representation of objects, thereby ruling out the possibility of knowing anything about them (the objects) prior to experience. This assumption opens the door to skepticism, as all knowledge of objects is held to be a posteriori (through experience of them) and therefore contingent (cf. Hume).
However, if, as Kant argues, the objects of sensation must conform to our active cognition (to "the constitution of our faculty of intuition"), then a priori, and thereby necessary, knowledge becomes possible through an analysis of this faculty and its forms.
Kant treats the status of concepts in a similar fashion. If, like intuition, concepts are assumed to conform to objects then we are once again barred from any a priori knowledge and skepticism looms. However, if objects conform to our concepts (which are generated in the interplay of the understanding and the "raw material" given in intuition) then a priori knowledge is possible through an analysis of the faculty and forms of intuition and understanding.
This Copernican reversal is not merely hypothetical as Kant attempts to demonstrate its merit apodictically in the Transcendental Aesthetic and Logic, respectively [see table of contents above]. In the Transcendental Aesthetic, sensibility is "isolated" [faculty of intuition] and two discoveries are made:
Firstly, that space and time cannot be merely empirical concepts derived from experience. For in order for the impressions of the senses to be distinguished from the subject as "outer" (as "objects" distinct from the "subject") or in any "relation" to enable a conceptual deduction of space, the representation of space must already be present in us and constitute the a priori ground of spatial determinations as such. Likewise, simultaneity and succession could not be perceived if "the representation of time did not ground them a priori."
Secondly, that the a priority of spatial and temporal representation, as forms of intuition, demonstrates that both space and time are necessary conditions for human experience and therefore are not, Kant claims, things existing independently of the constitution of our faculty of intuition. In this sense, space and time are empirically real; they are forms of the mind which hold sway in, and enable, all experience and empirical knowledge. They are therefore also transcendentally ideal; meaning, space and time are merely ideal (non-real) beyond the faculties of the mind.
continued below...


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First post: Formal Overview of the Preface
"For in [metaphysics] reason continuously gets stuck...we have to retrace our path countless times, because we find that it does not lead where we want to go, and it is so far from reaching unanimity in the assertions of its adherents that it is rather a battlefield, and indeed one that appears to be especially determined for testing one's powers in mock combat; on this battlefield no combatant has ever gained the least bit of ground, nor has any been able to base any lasting possession on his victory. Hence there is no doubt that up to now the procedure of metaphysics has been a mere groping, and what is the worst, a groping among mere concepts." B xv, Cambridge edition. (bold emphasis added)
Kant begins his 1787 Preface to the Critique of Pure Reason by comparing the fruitful progress of the sciences with the deadlock of metaphysics. Since the objects and areas of investigation of the sciences are fundamentally distinct from metaphysics (the latter being "a wholly isolated speculative cognition of reason that elevates itself entirely above all instruction from experience..."), Kant's comparison concerns the methodology of the sciences and what metaphysics can potentially learn from it.
In particular, Kant calls our attention to the work of Copernicus, whose advances in astronomy were made possible by uprooting and reorienting the fundamental assumptions of the field. Copernicus' progress came not by assuming, as was customary, a static observer around which the heavens revolve, but rather in interrogating the observer to see if, in fact, it was he that was in motion. It is in this sense, of a focal inversion from observed "objects" to the observing "subjects," that Kant's Critique initiates a "Copernican revolution" within philosophy.
The first steps in this transformation of the procedure of metaphysics consist in an examination of the traditional assumptions regarding the role of the observer/inquirer- specifically, the intuition of sensible objects (what is given in perception) and the nature of concept formation. Kant claims that until the Critique it was assumed that our cognition conforms to the objects of sensation [the Cambridge edition translates "erkenntnis" as "cognition", and so I also use it on occasion. However, it can also be translated as "knowing" or knowledge, which I usually find preferable to the very general and technical "cognition"; contemporary readers might interpret the latter as simply "thought" or some minimal mental event or process, which is not what Kant means]. Under this assumption, the faculty of intuition plays only a "passive" role in the representation of objects, thereby ruling out the possibility of knowing anything about them (the objects) prior to experience. This assumption opens the door to skepticism, as all knowledge of objects is held to be a posteriori (through experience of them) and therefore contingent (cf. Hume).
However, if, as Kant argues, the objects of sensation must conform to our active cognition (to "the constitution of our faculty of intuition"), then a priori, and thereby necessary, knowledge becomes possible through an analysis of this faculty and its forms.
Kant treats the status of concepts in a similar fashion. If, like intuition, concepts are assumed to conform to objects then we are once again barred from any a priori knowledge and skepticism looms. However, if objects conform to our concepts (which are generated in the interplay of the understanding and the "raw material" given in intuition) then a priori knowledge is possible through an analysis of the faculty and forms of intuition and understanding.
This Copernican reversal is not merely hypothetical as Kant attempts to demonstrate its merit apodictically in the Transcendental Aesthetic and Logic, respectively [see table of contents above]. In the Transcendental Aesthetic, sensibility is "isolated" [faculty of intuition] and two discoveries are made:
Firstly, that space and time cannot be merely empirical concepts derived from experience. For in order for the impressions of the senses to be distinguished from the subject as "outer" (as "objects" distinct from the "subject") or in any "relation" to enable a conceptual deduction of space, the representation of space must already be present in us and constitute the a priori ground of spatial determinations as such. Likewise, simultaneity and succession could not be perceived if "the representation of time did not ground them a priori."
Secondly, that the a priority of spatial and temporal representation, as forms of intuition, demonstrates that both space and time are necessary conditions for human experience and therefore are not, Kant claims, things existing independently of the constitution of our faculty of intuition. In this sense, space and time are empirically real; they are forms of the mind which hold sway in, and enable, all experience and empirical knowledge. They are therefore also transcendentally ideal; meaning, space and time are merely ideal (non-real) beyond the faculties of the mind.
continued below...