The Online Encyclopedia and Dictionary






Critique of Pure Reason

The Critique of Pure Reason is widely regarded as the philosopher Immanuel Kant's major work, first published in 1781, with a second edition in 1787.

Its original German title is Kritik der reinen Vernunft. It is also referred to as Kant's "first critique." It was followed by the Critique of Practical Reason and the Critique of Judgment. Critique in this context does not mean a negative attitude towards something, but a thorough examination of the properties and limits of something.

The Critique of Pure Reason is an attempt to answer two questions: "What do we know?" and "How do we know it?"

Kant approaches the questions by looking at the relationship between knowledge based on reason (what we know intuitively or a priori) and knowledge based on experience (what we know based on the input of our senses or a posteriori).

In Kant's view, a priori intuitions provide the framework that allows us to construct a posteriori knowledge. For example, Kant argues that space and time are not part of what we might regard as objective reality, but are part of the apparatus of perception.

In other words, space and time are a form of seeing.

When we see a box as three-dimensional, the shape of the box may not be part of the box's nature. Kant argues that our perception of the shape of the box comes from us, not from the box. Our perception IS the shape of the box, or vice versa.

The box as it really is -- the thing-in-itself or das Ding an sich-- is unknowable. For something to become an object of knowledge, it must be perceived, and the act of perception necessarily involves projecting onto the thing-in-itself our a priori intuitions. The act of perception changes the appearance of things-in-themselves.

That is, we are never passive observers.

Kant's argument is a precursor to Heisenberg's Uncertainty Principle and to Wittgenstein's arguments about the unknowability of the Self.

Kant's I—the Transcendental Unity of Apperception—is similarly unknowable. I might sometimes catch a glimpse of my I-in-itself, my ich an sich; my I as pure subject, as form but not as content. But no sooner have I glimpsed it than it disappears, because it cannot be an object of knowledge without content. And content is never pure or a priori. To know is to pollute. Only form is pure.

Therefore, we can never truly know ourselves.


Key Concepts

Transcendental aesthetic

Transcendental aesthetic is "the science of all the principles of sensibility a priori." In transcendental aesthetic, sensibility is isolated from all understanding, so that only empirical intuition is left. Next, all that belongs to sensation is taken away.

At this point, nothing remains but the a priori forms of perception, which provide structure to all perception. The two a priori principles of perception are time and space. No object can be represented without these principles, which neither "exist in the mind" nor are "properties of objects".

A difficulty in understanding Kant is the assumption that he accepts common taxonomies of thought and common dilemmas. The a priori forms of perception do not have to exist in the mind if they are not properties of objects and vice versa. Kant, ontologically creative, recognized a Third Way because the forms of sensibility ENABLE reflection on its content (which reflection "exists in the mind", of course) and apperception of objects (which, in an equally uncomplicated fashion, exist independent of and outside the mind).

Ruminating on Kant's method, a special-purpose machine designed as it were in the field and for the task, is important simultaneously to understanding his theses, for if the method is rejected or misapprehended, the theses reduce to nonsense.

A "timeless" perception in the sense of one so "instantaneous" as to have no (perceived) duration perception at all. We may question Kant about the inverse perception, of the same scene which is infinite in duration: wouldn't this be a perception after all? However, we'd still be aware of the passage of (infinite) time in this thought-experiment (and, die of boredom sooner or later); we cannot conceive of this experience unaccompanied by the passage of time.

It is likewise not possible to imagine a "spaceless" perception which isn't ordered in 2 or three dimensions.

Anglo-American philosophers commencing with Bertrand Russell have long objected to these arguments as being no more than rudimentary, amateur, parlor psychology. As crude gedanken experiments, so they are, and it is important instead to READ the Transcendental Aesthetic without such imagery. Kant, preparatory to the entire thrust of the rest of the Critique, was instead showing, by reduction to something less than absurdity, that we must retain certain abstract concepts in our ontology, not so much to avoid falsehood or even absurdity, but to enable the remainder of thought's apparatus to even get started.

And while Kant's arguments don't seem to violate the laws of syllogistic or ordinary modern logic, their "logic", even when labeled by Kant as "logic", is independent of and prior to "logic" whence the prefix "transcendental". Indeed, the "aesthetic" here has nothing to do with the philosophy of art (about which Kant had interesting things to say) but is a term of art and a label for what Kant felt was an epistemology unnoticed and unused by the skeptics...resulting in Hume's impasse.

It is thus a mistake to consider Kant an "idealist" and to classify him as a sort of ur-nineteenth century "idealist" or worse, along with Berkeley. Kant instead insisted that the bare possibility of perception, accompanied as it is by the continuing knowledge not only of its content but of self-identity over time of the perceiver, provides (as opposed to some sort of "skepticism") real, if "transcendental", knowledge of the world.

Kant called this a science because in his time, science was more or less cognate to knowledge, and had not become as it is today, knowledge plus procedure and even administration. Kant may be said to have thrown out the rule book because the very difficulty of the Critique is that it needs to make up the rules as it goes along, not our of frivolity but of utmost seriousness, for metaphysics, considered as a way-of-knowing, is in principle "infinite in all directions", admitting (unlike physics) no apriori limit to the invention, for which Kant is both celebrated and condemned, of tortured syntax and phrases, such as "transcendental aesthetic" itself, which are terms of art pari passu.


Immanuel Kant tended to use words in a somewhat unusual way. Understanding his terminology is critical for understanding his work. Key terms used in the Critique of Pure Reason include:


"Conception" is "the power of cognizing by means of these representations" which are received using the faculty of intuition. It is through conceptions that objects are thought.

Like intuition, conception can be pure or empirical. Pure conception contains "only the form of the thought of an object." Empirical conception requires the presence of an actual object. It is possible, in Kant’s view, to have conceptions of things that have no actual existence—such conceptions can only be pure, not empirical.


"Contingent" refers to a statement that may or may not be true without a contradiction. For example, the statement "Ralph Nader was not elected President in 2004" is true, but contingent. A possible world in which this statement is true can be imagined. Also see modal logic.

On the other hand, the statement "2+2=4" is not contingent, since its denial, "2+2≠4," cannot be true in any possible world.


"Intuition" is "the faculty or power of receiving representations"(see Second Part, Transcendental Logic, Of Logic in General). Objects are given to use through intuition. Intuition can be pure or empirical.

Pure intuition contains the a priori forms under which objects of senses can be intuited—such as the space and time. Without these a priori forms, objects of senses cannot be perceived or thought of. Pure intuition is only possible a priori.

Empirical intuition includes sensation—which presupposes the actual presence of an object. It is only possible a posteriori.

See also

External links

Last updated: 10-26-2005 07:16:43
The contents of this article are licensed from under the GNU Free Documentation License. How to see transparent copy