Immanuel Kant on the Perception of Space and Time.

In the Critique of Pure Reason, which is regarded as one of the most difficult books ever written, the philosopher Immanuel Kant (1724-1804) argues that space and time are not features of the world-in-itself but forms of intuition inherent in our faculty of sense.

In short, space and time are mind-dependent matrices for organising sense experience. Space is the pure form of “outer sense” by which we perceive objects as external and spatially arranged. Time is the pure form of “inner sense” by which we order our mental states. Because space is a form of intuition and not a property of the world itself, we are able to identify its structures à priori, independently of sense experience, as when geometrising.

Kant’s Amazing Insight

There is such a thing in nature as handedness, or chirality. For instance, in most people, the hair whorl on the crown spirals clockwise, from left to right. Hops wind clockwise, beans anticlockwise. Most snails coil clockwise, though a few species are predominantly or exclusively sinistral. Many molecules exist in both right- and left-handed variants. With thalidomide, it is only the S-enantiomer that leads to birth defects.

Kant had the amazing insight that no amount of verbal description can capture the difference between “incongruent counterparts” such as your right and left hand. What distinguishes the two can only be grasped through sensible intuition, which is tied to a conscious, embodied being’s subjective frame of reference.

Kant used this analysis of incongruent counterparts to bolster his argument that “space in general does not belong to the properties or relations of things in themselves.” 

The Mysterious World-in-Itself

Space and time are like the irremovable spectacles through which the human mind sees the world, and without which it would not be able to see it. Thus, as far as humans are concerned, space and time are not subjective but objective, insofar as they are “built-in” and common to all. If you are human, there is simply no other way of seeing the world.

This notion that objectivity is based on inter-subjectivity is one of Kant’s most important principles, underlying not only his metaphysics and theory of knowledge, but also his ethics and aesthetics. For instance, when making ethical decisions, we ought to abstract from our individual circumstances and proclivities and reason like any and every rational mind. When making ethical decisions, we seek to become everybody—to become pure mind, like God.

At this point, you may be asking yourself, if space and time are not features of the world-in-itself, what remains of an object, say, a tree or a table, outside of space and time? For Kant, the nature of the “thing-in-itself” [German, das Ding an sich, or noumenon] is entirely beyond the bounds of human knowledge. All we can say—contra Bishop Berkeley, who held that things are nothing more than perceptions in the mind—is that it exists in some form.

Could Kant Be Right?

A criticism of Kant’s general stance, which is known as transcendental idealism, is that we ourselves are objects in the world: our very existence and make-up presuppose space and time—which are therefore not “of the mind.”

Kant’s response is that human beings have a dual status. The phenomenal self is indeed a part of the phenomenal world. But the “I think” that makes experience and self-consciousness possible is not. This so-called noumenal self is the source of rationality and morality, and, because it stands outside of nature and contingency, of freedom as well. Our dual status is how we can still be morally free and responsible in an otherwise determined universe.

Kant thought of space as Euclidean. The later development of general relativity and non-Euclidean geometries, with their implication that space is not uniform, undermined Kant’s notion of space as an intuition—even though the human intuition of space might still be Euclidean.

Neel Burton is the author of the newly published The German Greeks: German Philosophy and the German Philosophers.