As I continue my deep read of Kant's first critique, I'm struck by the fact that both space and time are a priori concepts, known to us prior to any experience, CPR(A) Transcendental Aesthetic, S.7 p.39-40. But so too are the 12 categories in his framework. To be pure concepts, he tells us, they must also be a priori. CPR(A), Transcendental Logic, S.10, p.78-79.

What is the operative relationship among Kant's a priori elements?

A skeptic may ask whether is matters. But it matters in my analysis because I am trying to understand whether the nature of the 12 categories are essentially equivalent to space and time, or somehow derived from them.

In his first critique, space and time are "two totally distinct kinds of concepts" and specificially describes them as "forms of sensibility", whereas, in the same paragraph the categories themselves are "concepts of the understanding" CPR(A) S.13, p.85-86. This takes me down the path of separateness. And yet, as a priori concepts, there is a sameness that to me makes them function in a similar way, generalized abstractions with which we can categorize and frame our knowledge.

What guidance is available on this?

5 Answers 5


The following is explicitly a synopsis of the CPR only to provide a background and give basic insight necessary for understanding the answer to the question. Some points are slightly modified or amended in later works.

On the transcendental method in the CPR

Kant goes through our three faculties of knowledge (Sensuousness, Understanding, Reason) in the Transcendental Aesthetics, Analytics and Dialectics. In every faculty he is searching for transcendental a priori, which means nothing more and nothing less than the necessary conditions of the possibility of (this aspect of) objects of experience (see Prolegomena, 4:473f. fn.). Insofar it is possible, the a priori insights are established as real beyond reasonable doubt in the Transcendental Deduction (for more on how a priori knowledge is established in Kant, see this answer of mine).

On the different a priori for the three faculties of knowledge

For the faculty of Sensuousness, the faculty through which we acquire content, he says that the content needs to be ordered in the Space and Time in order for us to be presented with different (space), persistent (time) objects of experience at all (as opposed to a single, multimodal manifold). Thus, space and time are the transcendental forms of Sensuousness.

For the faculty of Understanding, the faculty that subsumes content under concepts, he says that there are fundamental conceptual categories that allow us to conceptualise objects and their relationships in the first place. These categories are, therefore, transcendental concepts.

For the faculty Reason, the faculty of inference from what is to consequences and conditions, he says that there are ultimate conditions of the experience of objects itself. Those are, according to him Soul, Freedom, God: The soul as ultimate condition of the unity of subjective experience (the self), Freedom as ultimate condition of the unity of objective experience (the world that includes all causal conditions of objects from its very beginning), and God as ultimate condition of the unity of being and thinking itself (harmony of subjective and objective experience). Since they are projections of our thinking that are thought to be the ultimate conditions, he calls them transcendental ideas.

On the commonalities, differences, and relations between the transcendental forms, concepts, and ideas

Transcendental a priori are all of them in the sense that they are necessary conditions of our relationality to objects of experience (question from his letter to Herz from 1773). They are not thought nor known "before" any experience in a sense of time, but in a sense of inference: Without them, our experience (or thought) would not be possible. It is a common, yet mistaken interpretation to say that we are born with an inventory of a priori knowledge. Otherwise, it would not have taken some thousand years to work them out, right?

Only space, time, and the categories do have corresponding objects of experience (i.e. every sensual intuition) and are therefore knowledge a priori proper. The transcendental ideas are presented as necessary end points of the search for end points in inference chains but as they are outside of experience proper and not about the forming of objects of experience, they are only problematic and not knowledge. The highest level of "confirmation" for them we get is that they are able to be thought without contradiction (definition A254|B310). Note that he changes that in his second Critique at least pragmatically, ie. establishes them as real in the sense of a real aspect of human action: they are realised in action but still not known in the same sense as objects of experience as we got no way to perceive them.

Regarding the relation between space and time on the one hand and the categories on the other hand there is another aspect already established in his dissertation and repeated in the Transcendental Deduction: Time and space as forms of intuition are used for the conclusion that sensual intuitions are appearances (in the sense of a way to represent the objects that are sensed) since we do know that they are aspects of our way of representing things but we cannot know inhowfar this representational mode has correspondence in the represented objects without being represented in a conscious mind.

What is new in CPR is that Categories are the most abstract concepts of relations between objects of sensual experience (which can only be given via intuitions!) and thus can only be applied to intuitions. Therefore, the form of space and time, as forms of intuition are "logically prior" to the categories as well. How could we differentiate unity and multiplicity without differences in temporal and spatial loci, which are necessary to have a definite object of representation in the first place, after all? In the same sense, the transcendental ideas are at the end of logical priority: only given we have established different definite empirical objects and the relations between them, we can start to bother about the grand picture and whether their relations point us to some common, ultimate condition.

I suggest reading Eckart Förster's The 25 Years of Philosophy for a quite good presentation of the overarching argument.

  • Helpful @PhilipKlocking .. especially the thought of space/time and the categories sequenced not in time, but to enable inference. Establishing conditions ..
    – sourcepov
    Dec 15, 2015 at 1:34
  • @sourcepov Did a major overhaul, maybe it now fully answers your question.
    – Philip Klöcking
    Nov 26, 2022 at 21:18

Space and time, for Kant, are essentially different but interdependent; they're essentially different from the categories - if the word essential is to retain its meaning.

The categories derive from Aristotles as a way of categorising the things that are; they're part of his onto-logic.

Kant reconceptualises them within his critical philosophy so that science, that is objective knowledge is possible; because science deals with things that are; this is his answer to Humes critique of induction.

I'm not sure that they need to be known to us in some specific order; but certainly Kant introduces them in a certain order because he's building up a system step-by-step; I expect he uses the forms of space and time in transcendental deduction that justifies his conceptualisation of the categories.

  • .. yes, conditions that help Kant build the case. The essence of each pure concept is different, but connected as part of the framework. An ontology of abstraction perhaps? It may be interesting to circle back to Aristotle's 10-15 predicables, as I believe Kant describes them, just to survey the raw material. I'm still learning how the categories operate. I understand the break down of his 4 class groupings, I think .. but not yet the relationships .. the verbs betwixt them.
    – sourcepov
    Dec 15, 2015 at 1:46

Hope this guidelines help:

  1. Space/time are not concepts but intuitions or forms of sensibility. Experience is only possible insofar such forms of sensibility are possible. Only then can concepts be possible.

  2. The Transcendental Aesthetic allows the possibility of concepts in the Transcendental Logic (understanding), concepts are not part of the former condition.

  3. The Transcendental Aesthetic allows experience, it is not previous to experience (just in case you mean "prior to" = "previous to").

  4. Categories are not equivalent to space/time, consider this: the Transcendent Aesthetic is the context allowing the possibility of experience; The Transcendental Logic is the context allowing the possibility of objects (Transcendental Analytic: simple, apodictic objects; Transcendental Dialectic: organic (organon), rational/ideal objects).

Strictly, the three/four Transcendental xxx are not layers, phases, stages or steps: they are not sequential, although they are linearly dependant. They must be considered as contexts of possibility or conditions of possibility, each one allowing the possibility of the next. In each context, something is produced that allows the possibility on the following one.

Example: A circle cannot exist without a surface; from a Transcendental Aesthetic perspective, a surface must be possible a priori for a circle to exist. Only then the categorized concept (in the Transcendental Analytic context) (singular, affirmative, apodictic, categorical) is possible.


It seems to me that Kant wants to say there is something intuitively given even before we think about it or conceptualize it. As an intuition, a form, space and time are just there. Imagine something in your head, say your pet dog or cat, and space and time are just there even though you aren't thinking of them, you are thinking of your cat, dog, hamster. Nevertheless, we have to have a way of talking about these intuitions, and in order to do that, we must conceptualize or represent them. But the concept of time is not itself time.

  • That is explicitly not what he wants to say. We learn to process input gradually and only later learn to conceptualise them and think about these processes, one of the highest grades is what his philosophy does. This only becomes more clear in his later works (esp. Anthropology), though.
    – Philip Klöcking
    Nov 18, 2022 at 12:06
  • I just want to clarify that when I say space and time are "already there," I don't mean that Kant is saying they exist in themselves, but that to the extent they are a contribution of our sensible faculties, they are spontaneous contributions, i.e, intuitions as opposed to concepts, at least in their pure form.
    – Gerry
    Nov 19, 2022 at 20:19

Responding to a line in Philip's excellent synopsis, in which he refers to mistakes interpretations of Kant's categories. "It is a common, yet mistaken interpretation to say that we are born with an inventory of a priori knowledge. Otherwise, it would not have taken some thousand years to work them out, right?"

Kant's introduction states that something is awakened by experience, but he does not say that that something are the pure concepts themselves but rather a "faculty" is awakened, which may be the condition for the "inference." But then when we say that a pure concept, e.g., Unity or Plurality, is inferred, do we mean that it discovered through inference? In which case, the concepts were laying in wait, somewhere, to be discovered, or by inference do we mean that the concepts are in some way synthesized along with the objects they are related to, which would indicate that our mind constructs them, or are they pre-existing synthetic forms, lying dormant, waiting to be used in the process of synthesizing objects, which would imply they are built in and waiting to be awakened.

"There is no doubt whatever that all our cognition begins with experience; for how else should the cognitive faculty be awakened into exercise if not through objects that stimulate our senses and in part themselves produce representations, in part bring the activity of our understanding into motion to compare these, to connect or separate them, and thus to work up the raw material of sensible impressions into a cognition of objects that is called experience?" (B1).

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