Is there a name for skepticism about the existence of categories (or properties) and objects that the mind may create to classify the "real world"? In other words thoughts, concepts, and so forth may conveniently classify the real world and help us predict things but they are only representations of the real world constructed from any sense data that we receive. It may correspond to objects in the real world but it is one step removed. So in this sense they do not exist (or rather, this position defines what exists to be everything outside the mind).

For example, the object tree only exists because human minds are calling some entity in the real world a tree. But if there were no human minds at all there would still be the thing we call a tree, it just would not have an actual name or identity at all. It would exist independent of human thought. Extending this, mathematical objects do not exist either but may be considered a model for the real world insofar as it reliably predicts our interactions with it.

Is there a version of this kind of position (more well-formed than my description) that describes this kind of view? The closest I can think of is perhaps a form of Platonism and sort of physicalism which acknowledges that we cannot know things-in-themselves ("real world"). It is opposed to solipsism or subjective idealism.

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    External Realism according to Buttons in his book The Limits of Realism.
    – Philip Klöcking
    Commented Jan 11, 2018 at 22:38
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    The view you describe is called nominalism. This is the idea that our words do not pick real categories in the world. It is actually opposed to platonism, which would say that these categories are real and correspond to ideal entities in an abstract realm. Commented Jan 14, 2018 at 20:00

2 Answers 2


The categories of thought clearly exist in a sense but it is a common view that they do not go all the way down, such that they would have to reduced for a fundamental theory. They would exist conventionally, (like money or democracy) but not metaphysically.

This would be Kant's view and is more generally that of what has come to be known as the Perennial philosophy or mysticism. Any doctrine that endorses the Unity of the Universe will depend on the metaphysical unreality of the categories of thought or, rather, the objects so categorised, since Unity may be achieved only if all distinctions and divisions are conventional and reducible.

The situation is difficult linguistically since for this view the creations of mind can be said (clumsily) to not-exist, but at the same time they would be the only phenomena that (seem to) exist. It's the use of the word 'exist' that is tricky and for the perennialist this means using a language of contradiction, as we see from the famous comment of Heraclitus 'We are and are-not'.

For a proof that the categories do not exist except conventionally such that nothing really exists or ever really happens there is Nagarjuna's Fundamental Versus on the Middle Way and FH Bradley's Appearance and Reality. Their view may be called 'nondualism', 'transcendental idealism', 'absolute idealism' and other phrases. It is the philosophy of the Upanishads, Lao Tsu and the Buddha. Christian and Islamic mysticism and much more. Some say it is what Jesus and Mohammed taught. In metaphysics this view requires a 'neutral' metaphysical position, one that denies the truth of all positive or extreme positions (all of which are require a reification of the categories of thought).

It is, however, an heretical idea in Western thought and not well-known. Kant is about as far towards this view as most university philosophers seem prepared to travel and there is a serious lack of scholarship in the department in respect of the view you are asking about. For an introduction Bradley's Appearance and Reality is a wonderful read, elegant and profound, and it sketches out a proof.

No student of philosophy should need to ask your question but what is taught in our universities is an idiosyncratic view of philosophy that ignores large parts of it.

  • I do not think what I am describing fits exactly with idealism or nondualism. It appears to us that "we are" because our brains give that appearance. Conventionally and practically, that is reality. I am not saying that "nothing really exists [or] happens" but that the mental reality as we perceive it is an approximation of an otherwise elusive reality that exists outside. We can come to understand aspects of this reality through empirical measures like science but we may not be able to actually perceive/experience it as it really is - we perceive it only as our brains interpret it.
    – syntonicC
    Commented Jan 23, 2018 at 15:22
  • Consider metamerism. What is "real" is an object with specific properties that we call photons in scientific terms. Our eyes take in some of this information and perform what can be mathematically described as a linear projection onto three dimensions (RGB) which throws out data. This, with other information (shadow etc) forms a representation of what is there. It's obviously good enough but what we end up perceiving isn't actually "real" as defined in my description above. This seems different from idealism but maybe I've misunderstood you.
    – syntonicC
    Commented Jan 23, 2018 at 15:36
  • Your view is quite common I think but as you say, idealism goes further and suggests, pace Kant, that the material world is a creation of Mind and that the 'I Am' of consciousness is not brain-dependent. Perhaps the difference is that your view works just fine in everyday life while the more drastic view also works in metaphysics. It's a fun puzzle that we all have to try to solve for ourselves. .
    – user20253
    Commented Jan 24, 2018 at 13:12

This is most succinctly captured in modern analytic terms as 'supervenience of the ideal upon the physical.' It is one form of 'emergentism' as a theory of mind, which identifies concepts as emergent phenomena of our social interactions (via Wittgenstein's language-games or some similar social construction), and therefore of our biological processes, which are ultimately physical processes.

This perspective allows for the 'mind' (and in the process 'life') to exist and have contents, but only as a process entirely derived from physics, even though parts of it are not tractably reducible to the processes from which they derive.

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