Kant on Space and Time – 13/06/2016

time and space

“Space is not objective and real …; instead, it is subjective and ideal, and originates from the mind’s nature in accord with a stable law as a scheme, as it were, for coordinating everything sensed externally.” writes Immanuel Kant (1724 – 1804) in his Inaugural Dissertation (1770).


Yes, you read that correctly: space is not real. That is exactly what Kant is saying. But what does he mean?

When we think about space and time, it is useful to consider a couple of distinct questions:

  1. What are space and time? In what way do they exist? (an ontological question)
  2. How do we represent space and time in our mind? How do we think about space and time? (an epistemological question)

Let’s start with the first question: what are space and time? For Kant, the answers available at his time made this a multiple choice question:

  • A. Space and time are substances.
  • B. Space and time are properties of substances.
  • C. Space and time are not properties of objects, but still dependent on objects for their existence.
  • D. Space and time are not substances, but still exist independent of other objects. Or,
  • E. Space and time are not real.

Space and time can hardly be substances themselves. They do not take up space or time (as they are space and time) and they are imperceptible. They are causally inert: they do not change at all when they interact with other substances. Are they properties of substances, then? Just like red is not a substance – it does not exist on its own – but a property of substances – other, independently existing, substances such as apples and books can have red as a property -, perhaps space and time are like red in this respect: a property. Apples and books can be red, blue, big, small, round, square or… spacial and temporal. So perhaps substances exist first, and then space and time are merely properties of those substances? But that is problematic too. That would suggest that the existence of space and time is dependent on the existence of substances. Moreover, if they are properties, then they could fail to exist even when there are substances. If space and time exist, it seems that substances exist in space and time, and not the other way around.

Perhaps, then, space and time are relations between objects. There’s an apple, and a little later I place another apple about three inches next to the first apple, and space is one way in which both apples relate to each other (there is space between them) and time is another way in which they relate to each other (some time passes between the placement of each apple). But this raises a similar problem: this would imply that space and time do not exist independent of objects such as apples. This is a problem, because we would normally imagine that space is what apples are in. That is to say, each spacial object – such as an apple – takes up space, regardless of whether there is something else next or behind or above it. If there were only one object in the entire universe – say, an apple – and nothing else, then everything around it would simply be empty space, not no space.

So, if space and time cannot be dependent on the things that exist in space and time, then they must either exist, in physical reality, independently of any object, or – option E – space and time are not real, that is, not part of reality that exists independent of our knowledge of it. Kant thinks the correct answer is the latter: space and time are not real.

To explain why Kant thinks that space and time are not real, we’ll have to turn to the second question: how do we think about space and time? How do we represent them in our mind? According to Kant, space and time are pure intuitions. They are categories of the mind, which the mind imposes on our perception in order to be able to perceive anything at all. Space and time exist only in our minds.

You may find this an odd idea. Surely, space and time are real and have always been part of reality, even before there were minds. The Big Bang happened long ago in time and ever since the universe is exploding, growing bigger in space. There weren’t human minds back then, so surely, space and time are not dependent on our minds!

Indeed, that was the prevailing philosophical stance in Kant’s time too. The Empiricists believed that we get to know about space and time through experience. We see an apple, and another apple a few inches further away and that’s how we get the idea of space. Likewise, we have an apple, then we eat it, and then we are left with only its core. Experiencing a succession of events like that is how we learn about time. That, very briefly, is how the early modern Empiricists believed we acquire the concepts of space and time.

But not Kant. Kant flips this picture upside down. According to Kant, space and time are not even concepts, they are pure intuitions. Intuitions, according to Kant, are representations in our mind of singular, particular things to which we have immediate access. Concepts, on the other hand, are representations in our minds of generic classes of things, which we have acquired through learning of some kind. We can have an intuition of this particular apple in front of us, but not of apples in general. We have a concept of apples in general, and at any time, whether we have an apple in front of us or not, we can imagine this concept of apples along with the characteristics we have learned about apples. Space and time, on the other hand, don’t work like that, according to Kant, they are pure intuitions. We can only ever think about space and time as singular (space can be divided up into smaller sections, but it remains one big endless space, and the same counts for time) and we have immediate access to it: we needn’t learn anything about space and time, we always intuit them already. In fact, says Kant, we cannot imagine anything at all without imagining space and time along with it. We are simply unable to imagine spacelessness and timelessness.

Space and time, therefore, are categories of the mind, according to Kant. They are features of the mind that enable us to experience anything at all. Our mind apply space and time to our experience of reality, because otherwise we would not only fail to make sense of it, but we would fail to experience anything whatsoever.

Try it. Imagine an apple. Now imagine an apple without space. You can’t do it. Imagine a timeless apple, not an everlasting or eternal apple, but really a timeless apple. One that exists without there being any time during which it exists. Can’t be done. It’s easy to imagine things without apples, but as soon as we imagine anything, as soon as we represent anything in our mind, we must also imagine time and space at the same time.

Now, why is it impossible to imagine anything without space and time? Because space and time are always there, have always been there, and we’ve always experienced space and time, one might answer. But Kant doesn’t think so. Remember, we cannot actually perceive space and time. They are imperceptible. You don’t see space: you see things in space, but not space itself. You don’t feel time, you feel all sorts of things happening in time, but not time itself. Yet, we cannot see or feel or hear things without having an immediate intuition of space and time also.

This means, according to Kant, that our knowledge of space and time must be a priori (before experience), instead of a posteriori (after experience). Geometry, for instance, would not be able to make any progress if space were not known a priori. Geometry is not an empirical science: we don’t go around trying to find lots of triangles to test empirically whether the sum of their angles is indeed 180 degrees. Instead, geometry provides us with the knowledge that the sum of the angles of all triangles is 180 degrees purely with knowledge that is in human minds already: knowledge of space.

Therefore, according to Kant, space and time are features of the human mind, not of reality. They belong to the world of ideas rather than reality, so space and time are not real but ideal.

“But that is ridiculous,” said one of my students when I had explained this in a small group seminar, “how can space and time not exist in reality? That is just bizarre.”

“Of course!” I said, “Of course it’s bizarre. That’s exactly what Kant expects you to say, isn’t it? If space and time are how your mind enables you to experience anything at all, of course it would strike you as bizarre to suggest that space and time do not exist! That’s precisely his point.”

This view on space and time forms part of Kant’s bigger project: to show that we cannot acquire knowledge about things as they are in themselves, but only about how they appear to us. Since how things appear to us is determined by the mind – which, according to Kant, applies 12 categories in total, of which space and time are two – we can only acquire knowledge by means of reasoning. This makes Kant a rationalist as opposed to an empiricist. Kant’s view, that the mind determines what we can know by determining our perception, is called transcendental idealism. There will be more lessons on Kant to follow.


You can find Kant’s Prolegomena For Any Future Metaphysics here. It’s a short piece, difficult, but worth reading.

This video explains how Kant uses geometry to make his case that space is only in the mind:

And here’s a song about Kant:


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