I've been trying to explain Kant's transcendental idealism to a friend of mine. By transcendental idealism I am referring to a world of appearances which receive their character from the point of view from which they are seen (Kant's categories). I briefly went over Kant's subjective and objective deductions to demonstrate this. I talked about, as an example, that the world and the mind both obey non-contradiction (you could not imagine or experience/see a car that was both blue and not blue).

In response, he argued that there are plenty of things that we know exist in the world but cannot experience, bringing up the fifth dimension, for instance. Thus, he said, the objects/substances of the world are not a product of our minds.

How would Kant respond to this objection?

I asked a question like this a couple of days ago, but was too unclear about what I meant, misleading those who tried to answer me. So, I hope, this time I was clearer. Let me know if you have any questions.

2 Answers 2


There are no objects that exist but cannot be experienced.

This is actually the starting point of Kant's argument in the Critique of pure reason:

In whatsoever mode, or by whatsoever means, our knowledge may relate to objects, it is at least quite clear that the only manner in which it immediately relates to them is by means of an intuition. To this as the indispensable groundwork, all thought points. But an intuition can take place only in so far as the object is given to us. This, again, is only possible, to man at least, on condition that the object affect the mind in a certain manner.

And you can argue that this is true even for very complex scientific concepts:

Science is based on observation i.e. if I just sit at my armchair and theorize about the existence of a thing that does not make the thing exist. Not everything that can be thought exists.

In order for the thing to be accepted (or even considered) as existing, some evidence has to be observed i.e. the object has to "affect the mind in a certain manner".

Nowadays the way this is done in science is pretty complex: scientists use all kinds of tools to aid their observations, they use computers to analyze the results, but at the end of the day, the way that they acquire knowledge is not so different from the way people do it in their everyday lives - they observe and give names to things that they see.

  • He writes "the only manner in which it immediately relates to them" - the transcendental ideas are both real (since they are necessary for other things we do immediately experience) and cannot be experienced themselves.
    – Philip Klöcking
    Commented Feb 21, 2020 at 7:34
  • I don't think that Kant considers God and the Soul as real. For one they are covered in the chapter Transcedental Dialectic which Kant calls "the logic of illusion"
    – Jencel
    Commented Feb 21, 2020 at 21:22
  • It is a main point of the Critique of Practical Reason to prove the reality of Freedom, God and the Soul. Also, the transcendental ideas are contrasted with illusionary ideas in this chapter.
    – Philip Klöcking
    Commented Feb 21, 2020 at 21:30
  • Random quote from the chapter "Of the Impossibility of an Ontological Proof of the Existence of God: It is evident from what has been said that the conception of an absolutely necessary being is a mere idea, the objective reality of which is far from being established by the mere fact that it is a need of reason. On the contrary, this idea serves merely to indicate a certain unattainable perfection, and rather limits the operations than, by the presentation of new objects, extends the sphere of the understanding."
    – Jencel
    Commented Feb 21, 2020 at 23:22

I would argue that the discourse mixed very different understandings of "knowledge", "experience", and "existence".

In Kantian epistemology, there are "things" that we know to exist although we cannot possibly experience them: the transcendental ideas Soul, God, and Freedom.

Since they guide the understanding and are necessary for the synthetic union of experience as a whole (CPR A321|B378), things like the 5th dimension obviously are not transcendental ideas, but ideas nevertheless: ideas are concepts beyond possible experience (A320|B377).

Now, we should be careful what we mean with knowing to exist here. Existence in Kant is a messy thing in and of itself. But for the problem at hand, it might suffice to object that we "know" the fifth dimension (or quantum objects) to "exist" in a quite different way than we "know" the ball we catch to "exist".

When we speak of things like the fifth dimension or quantum objects, then these are either purely formal concepts (the fifth dimension is about solutions of mathematical formulae in theoretical physics as far as I am aware) or theoretical entities which serve as an explanation for certain empirical findings. Thus, they are how we imagine or theorise things to be. We do not exactly know that they exist the way we think them to be, but our models have proven to provide some predictive value, ie. practical usefulness.

Long story short: Theoretical entities may have heuristical value and empirical validity, but they are, themselves, not known to exist any more than alien life forms since knowledge, for Kant, involves much more than statistical probability and theoretical plausibility. As of the fifth dimension, this really is a bad example. It has no predictive value in terms of empirical events so far. Thus, it has to be considered mere speculation, not knowledge.

  • This makes sense, but I'm curious about one thing. These theoretical entities would still conform to Kant's categories, right? Commented Feb 20, 2020 at 19:50
  • It may surprise you, but I'd wager that they actually do not. While the table of judgements some pages beforehand is about "possible objects of thought", the table of categories is explicitly about "possible objects of experience". Therefore, my educated guess is that while they "could" and, especially in scientific context, usually do, they do not have to conform to the categories.
    – Philip Klöcking
    Commented Feb 20, 2020 at 19:55
  • Alright. So, does this not indicate a problem with the transcendental perspective? Transcendental idealism states that all objects receive their character from the point of view from which they are seen. This is why he argues that we cannot make any judgements about things that exist outside the limits of bounded human experience. Yet, certain quantum objects exist outside these limits and we can make some judgements about them (even if they're just statistical probability or theoretical plausibility). Commented Feb 20, 2020 at 20:05
  • @BrockNykoluk Kant turns against speculative philosophy (Leibniz, Wolff) here and explicitly writes about judgements about things that are known to be real, ie. exist (see Prol. 4:373 fn). The problem here is that both we have - in some sense - empirical experience of quantum objects (experimental evidence) and at the same time all the evidence is data interpreted on the basis of theoretical hypothesis, ie. we do not exactly know that what we measured is the quantum object and what it is, the data just happens to fit whatever we conceptualized as quantum object with certain properties.
    – Philip Klöcking
    Commented Feb 20, 2020 at 20:11
  • I was hoping you'd answer this. I'd like to clarify one thing. Theoretical posits of physics are much more intimately related to empirical experience than the nebulous noumenal posits released from the schematism and the categories. Quantum objects are located in space, for instance. Meillasoux took this to a logical conclusion: declaring fossilized animals to be just explanations for empirical findings that exist in a different way is not too attractive. I wonder if Kant has resources alternative to biting the bullet here. Elaborating on how new empirical concepts come to be, perhaps?
    – Conifold
    Commented Feb 20, 2020 at 23:04

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