Kant’s Critiques
The purpose of Kant’s critique is to inquire whether rational metaphysics is possible. Is the project, on a rational basis, which Descartes began possible?  Is the project, on an empirical basis, which Locke began possible?

1) Critique of Pure Reason (1781)
Theme: the faculty of knowing; TRUTH.
“Critique of Pure Reason” (CPR) is known as Kant’s best work. Kant builds on the work of empiricist philosophers John Locke and David Hume as well as rationalist philosophers Gottfried Leibniz and Christian Wolff. CPR was poorly reviewed and dismissed as "a system of transcendental or higher idealism" – the critique of the ‘Critique’ being that the account of things exist beyond all experience (Kant challenged the scientific empirical viewpoint of reality).  Further, CPR is not an easy read. Some have expressed that Hume's works have had a more lasting influence – his works are easier to read and digest. In short, the bulk of CRP is concerned with how a priori knowledge is acquired and the belief that the subject imposes rational a priori concepts of understanding upon sense-data. ‘Pure’ in Kant’s language means a priori.

In 1783 Kant published "Prolegomena to Any Future Metaphysics that Will Be Able to Present Itself as a Science" as a rebuttal, and summary to CRP, where he argues that his intent is to restrict his investigation to experience and the knowledge that makes it possible.

CPR is a critique of using only pure reason. This is opposed to using empirical evidence, which is what we perceive, the relations of facts, or empiricism. In explaining how objects are experienced Kant uses conceptional transcendental arguments which begin with the indirect examination of perceived objects.  In contrast, Arthur Schopenhauer ('The World as Will and Representation', 1818) begins with a direct examination of perceived objects where abstract concepts are not the starting point of knowledge. Schopenhauer generally objected to Kant's methodology, however he did accept many of Kant's conclusions such as his description of experience and its relation to space, time and causality.  Michael Kelly, in the preface to his 1910 book ‘Kant's Ethics & Schopenhauer's Criticism’, stated: "Of Kant it may be said that what is good and true in his philosophy would have been buried with him, were it not for Schopenhauer...."

CRP was born out of Kant’s ‘awakening from his dogmatic slumbers’ from the works of Hume. Kant’s awakening ‘Ah-ha’ moment was the realization that knowledge from experience is not necessarily grounded in experience. That there is a difference between something arising from something else and something being based on something else.  Kant points out that Hume's thesis about causal concepts (ie, A is the cause of B) did not consider TIME. That you cannot get any events in experience at all, located in time, unless time, as a categorical framework for experience, is already in play. According to Kant, since time is not a stimulus that works on a sense organ it cannot be provided by experience. All experience presupposes a spatial, temporal framework.  There cannot be experience except by way of time and space.  Kant refers to these as the “Pure Intuitions of Time & Space”.  Time, as being non-empirical, is not a something 'out there' that stimulates one.  All temporal experience relies on the a priori, necessary preconditions of Time & Space.

CPR has three major sections. The first two deal with epistemology and the last with aesthetic. In sections 1 and 2 Kant informs that knowledge only extends to phenomena - appearances. Rather than the things in themselves - noumenon – what he calls the true ‘reality’.
Section 1-Transcendental Aesthetic.  The ‘Aesthetic’, in general, has nothing to do with the arts (beauty).  It deals with sense perception or the faculty of sensing.  Kant describes space & time as an a priori notion (the ‘Pure’) where the ‘pure forms of intuition’ create the preconditions for objects to appears. Space & Time are not objective realities; not ‘things’ but abstractions or concepts. The only meaningful way to talk about space is when there are physical events occurring and there is a spatial relationship between them. 
Section 2-Transcendental Analytic. The ‘Analytic has to do with the positive role of reason, the principles of understanding and the faculty of thinking. For Kant the term ‘analytic’ means ‘taking apart’ which is what he attempts to do when he analyzes the question “How are synthetical judgements a priori possible?" which was not possible in Hume’s worldview. Kant’s insightful examples of the synthetic a priori statement is E=mc2 or spacetime – true, but we can’t confirm them with direct experience.
Section 3-Transcendental Dialectic. Kant’s final section deals with opinion and belief.  There are two kinds of beliefs: 1) Doctrinal, 2) Moral.  Doctrinal beliefs cannot be proved. Moral belief is based on action – “I must obey the moral on all points” (Kant’s Deontology).  What Kant does in the dialectic is to examine dialectically the arguments that metaphysicians put forth regarding the metaphysical triad: Mind, Nature, & God. At the end of CPR Kant tells us that we cannot demonstrate the existence of God. However, he asserts that it may be possible on the basis of ethics to rationally affirm the existence of God which leads into Kant’s next Critique.

2) Critique of Practical Reason (1788)
Theme: the faculty of willing; GOODNESS
Kant’s second Critique concerns moral will, moral responsibility and moral duty. Also, about vice and virtue and that his Categorical Imperative tells us how we can distinguish between right and wrong.

Bringing Morals Back to the Center Stage
Late 18th-century was a period where materialism was on the rise.  The aftermath of the scientific revolution - the Copernican Revolution - was a turn toward a mechanistic science without teleology: a reason or explanation for something became a function of cause as opposed to its end, purpose, or goal. This in turn fueled a moral crisis that forced many to look for new ways of addressing ethical questions. Kant was a moral realist. He was trying to avoid some of the possible ethical implications of the mechanistic science with its causal determinism which takes away individual moral responsibility.

3) Critique of Judgment (1790)
Theme: the faculty of feeling; BEAUTY.
Critique of Judgement is divided into two main sections: the Critique of Aesthetic Judgment (taste, quality, the beautiful) and the Critique of Teleological Judgment (judging things according to their ends).

Kant & the Golden Seat
The Golden Seat has a representational structure to Kant’s Critiques:
 The Legs: Beauty (#3), Truth (#1) & Goodness (#2)
 The Seat: God, Spirit

In Closing

The skeptic, wakes up from his ‘dogmatic slumbers’, crushes out his Morely, and asks Kant:
Skeptic: “How good is phenomenal knowledge as a representation of what is noumenonally real?”,
Kant: “You’ll never know”.

The skeptic fires up another coffin nail, draws in philosophically, and presses the point:
Skeptic: "Then how do you know there really is a noumenomal realm?".
Kant: "From the very fact of phenomena, it follows that there must be some noumenonal existence behind these phenomena". 

What Kant is trying to explain is that there is something reason itself can reach. So, reason can inform us that there is a noumenonal realm, but reason cannot tell us what that noumenonal realm is.  We know ‘that it is’, we don’t know ‘what it is’.

The skeptic lays down his cigarette; mysteriously a question mark rises…