Suppose I say, "There are no noumena." How can I be proved wrong without any doubt?

  • There is always doubt. We must deal instead with where the weight of evidence lies. In particular, we seek the simplest explanation that explains all our observations. It happens to be simpler to assume that there is indeed an external world; science depends on this, allowing us to form relatively simple rules that explain and predict much of our observations. Without an external world, observations would occur at random, unexplained, without any simple unifying principles. This is a basis to prefer the idea of an external world.
    – causative
    Commented Oct 30, 2023 at 4:58
  • How do you define noumena?
    – Jo Wehler
    Commented Oct 30, 2023 at 5:06
  • @JoWehler as a thing as it is in itself. Commented Oct 30, 2023 at 5:12
  • 1
    "There's no noumenon" literally means "there's nothing that we don't perceive", which is obvious, for at least three reasons (surely there are more): a) we perceive only part of the world (not only due to distance, but due to size, time, depth, scale, etc.); b) our senses are limited (e.g. we can't perceive uv light, neutrons or thermodynamic microstates); c) reason cannot apprehend all facts of the world (knowledge from TV is a joke).
    – RodolfoAP
    Commented Oct 30, 2023 at 5:34
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    @DheerajVerma Since there are phenomena and noumenon due to the existence of the senses, then, there exists something to sense (so, it is your question that implies there exist "things outside our senses"). If you want an idealist perspective, the noumenon must be excluded from the question, the question is ill-formed if you assume a sensible world (Aristotelian physika), and that it can be perceived. Noumenon does not exist without phenomena, which can't exist without perception. You better ask yourself if you really exist and how.
    – RodolfoAP
    Commented Oct 30, 2023 at 7:20

2 Answers 2


The question considers noumenon as a synonym for a thing in itself in the sense of Kant's Critique of Pure Reaosn.

To negate the existence of noumena is the position of solipsism. There is agreement that one cannot disprove solipsism.

On the other hand it is a difficult task to develop an epistemology based on solipsism. I do not know whether it has ever been attempted. E.g., how does a solipsist explain the function of sense organs, which are normally considered the interface to an external world?

In any case, also a solipsist philosopher has to provide arguments which support his/her thesis. Just to negate is not sufficient.

  • I'm not sure solipsism implies the negation of the noumenon. If so, phenomena will also be denied (one cannot exist without the other). Even if I am a solipsist, there are facts I perceive about things (phenomenon) and facts I cannot perceive (noumenon). The fact that such configuration is just a product of my mind is another history.
    – RodolfoAP
    Commented Oct 30, 2023 at 7:35
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    @RodolfoAP A solipsist could characterize phenomena as autopoietic, i.e. as being spontaneously created by myself.
    – Jo Wehler
    Commented Oct 30, 2023 at 7:38
  • Exactly, so would be the noumenon. Ergo, it is not denied.
    – RodolfoAP
    Commented Oct 30, 2023 at 8:54

Jo Wehler is wrong. A solipsist would be someone who denies that he perceives external things but rather claims that he simply imagines them. Kant himself discusses such skepticism in his Refutation of Idealism where he claims it's actually unintelligible, at least given some considerations regarding time that follow from earlier parts of the Critique of Pure Reason.

The distinction between noumena and phenomena, things as they are in themselves and things as they appear (thus: things in themselves and appearances), is introduced at the very end of the Transcendental Analytic but is elaborated mostly in the Transcendental Dialectic.

The reason why Kant claims we cannot know things in themselves is because he stresses that thought acquires all content through sensory intuition where the act of reflective self-awareness and the very thought of an intuition are distinct. This isn't the case with concepts, judgements, inferences etc. Consider rule-following. Whenever I follow a rule, I am aware that I follow that very rule and this constitutes my following it. Hadn't I followed the rule, my actions could have been subsumed under many different rules which explain my behavior. This is what Kant means when he says that thought is spontaneous. It's not the same with sensory intuition which rests on something external, i.e. causal interaction between our sensory organs and external things.

It seems that rule thus acquires its content through itself, not from an external source. But Kant insists that this cannot be the case and that thought is always a synthesis or a combination of a manifold of intuitions, so that it is merely formal and acquires all content externally. And our, human intuition, is spatio-temporal (Kant considers forms common to objects of all senses but, of course, various senses have different formal objects). In sensory intuition, there is a distinction between things as they are in themselves and as they appear to the senses. Kant's claim is thus only that, because content for our thinking is given from another source, it doesn't have the absolute universality that thinking has and therefore objects that we can know anything about (here: know = have contentful thoughts) are not things-in-themselves.

You can clearly see why noumena (nous = thought, mind) are called noumena. They're the object of thought as such. An appearance is an object as it appears to, ex. human senses, according to some form. Noumena can, for the same reason, be also considered negatively, as what can be merely thought, but not known (to know = to have contentful thoughts about). That's more or less what Kant himself says in the Analytic.

If thought however was able to produce its own content, then we could speak, under Kant's terminology, of intellectual intuition. This is not some special intuition that is just not sensory, in our case: spatio-temporal, but rather the notion of thought producing its own content. In such a case, you cannot make a distinction between appearances and things-in-themselves, because you cannot say that the object of intellectual intuition is restricted to some formal characteristics, i.e. spatio-temporality, but is fully universal.

Kant's Transcendental Dialectic is quite straightforward then: it shows how pure concepts can acquire no content without sensory intuition. The dialectical contradictions which appear when we attempt to reason outside of bounds of experience are a sign (or so Kant thinks) of Kant's claim that we cannot have knowledge of things as they are in themselves, independently of the forms of our sensory cognition.

The German Idealists, beggining with Fichte (who was absolutely not a solipsist), immediately started to play with this idea. Fichte recognized that it must be possible to be self-conscious independently of sensory affection in order to be able to be self-conscious in this mannor (it's good to understand it by an analogy to another mode of self-knowledge: cannot really ascribe mental states to others without being able to ascribe them to ourselves). So, Fichte claimed, thought isn't always a mere combination of an already-present manifold of contents (although, of course, empirical knowledge - and thus most of our knowledge - is). Dieter Heinrich called this 'Fichte's original insight'.

To answer your question: The existence of things-in-themselves is, as I hope it's easy to see after reading my explanation, a pseudo-problem that doesn't make sense in Kant. Why? Whenever we think something, Kant says, independently of sensory intuition giving us testimony of its existence, we think its mere possibility. That's why, Kant explains, the ontological proof for the existence of God doesn't work. But in the case of intellectual intuition thought and its content aren't at all distinguished (think of Fichtean self-consciousness - being conscious of one's self-conciousness is the same as being self-conscious). Kant denies this is actually possible (unless we're God or something). So the noumenon remains an entirely empty notion. But, if it weren't an empty notion, we couldn't ask about its existence anyway.

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