Kant was always talking about the 'ding an sich', that we can't know what such a thing is in reality. But from Descartes we already have the thesis that we can only really know our perceptions, while it's uncertain whether the objective outer things correspond with them. It's true he suggested that because of God our thoughts about reality are correct, but physically speaking he would say that our mind doesn't have access to that world; if I'm right?

But was Descartes the first who said we don't have access to the outer world or was for example Democritus also speaking about that?

  • Where do you think Descartes says "it were only our perceptions we could really know"? Aug 30, 2016 at 19:19
  • For example in the 'THE PRINCIPLES OF PHILOSOPHY' number LXVI: 'There remain our sensations, affections, and appetites, of which we may also have a clear knowledge, if we take care to comprehend in the judgments we form of them only that which is precisely contained in our perception of them, and of which we are immediately conscious. " gutenberg.org/cache/epub/4391/pg4391-images.html
    – Marijn
    Aug 30, 2016 at 19:31
  • 1
    Unfortunately, Descartes's "explanation" turned out to be incoherent for two reasons. First was pointed out by Kant: he talks about reality "causing" perceptions, whereas on his own view "causing" only makes sense among perceptions. But then talking about "reality" distinct from them is meaningless. Second, even if we overlook that, as Hegel pointed out perceptions are not propositions but qualia, so we can not "know" them at all, only feel. Knowing requires bringing qualia under concepts, and this goes beyond perceptions. So Descartes's "perceptions" are as meaningless as his "reality".
    – Conifold
    Aug 30, 2016 at 19:53
  • You mean his explanation is incoherent for Kant and Hegel? But do you think that Descartes would agree with them and are they realy saying it right? Kant could have said that reality is meaningless, but is that true? Moreover wasn't the 'ding an sich' not a reality causing the perceptions? And aren't qualia more than just 'imprints'? And aren't qualia not a argument against 'type physicalism' saying that physical processes are different from our conscious with his concepts?
    – Marijn
    Aug 31, 2016 at 9:03
  • @Marijn No, I mean that it is incoherent on Descartes's own terms, Kant and Hegel only pointed out why. They did not think that reality or perceptions are meaningless however, only that the Cartesian conception of them is, what is now sometimes called the Cartesian theater en.wikipedia.org/wiki/Cartesian_theater A realist view that takes into account Kantian and Hegelian objections was developed by Sellars for example iep.utm.edu/sellars
    – Conifold
    Aug 31, 2016 at 16:10

3 Answers 3


You can trace Western skepticism about our perception at least all the way back to Parmenides of Elea, who posited that motion is impossible and that therefore our senses are illusory. There's a whole network of metaphysical reasoning invoked to argue for and support this claim, and it's been quite influential in the grand scheme of history of philosophy.

Parmenides then fostered the thought of Zeno of Elea, who is infamous for his paradoxes, and things have somewhat snowballed from there.


I do not usually quote from Wikipedia, but here it, well, fits..

Pyrrho (/ˈpɪroʊ/; Greek: Πύρρων Pyrrōn, c. 360 BC – c. 270 BC), a Greek philosopher of Classical Antiquity, was a student of Eastern philosophy and is credited as being the first Greek skeptic philosopher and the inspiration for the school known as Pyrrhonism, founded by Aenesidemus in the 1st century BC.

Pyrrho was reported, by his skeptic followers in later eras, to be the first philosopher who argued, directly and thoroughly, about our lack of ability to know reality as it is. This should be distinguished from:

  1. The common view, among ancient Greek philosophers, that we usually do not in fact know the true reality. By that it was not meant that reality was unknowable, just that it was usually not known as it is.

  2. Heraclitus's (~535-475 BC) view that reality itself lacked identity ("you cannot step into the same river twice") so that it could not be known, because there was nothing to know. And not because our cognition was somehow limited.

  3. Skeptical views among some of the sophists (known to us especially from Plato's dialogues), notably Protagoras (~490-420 BC). Protagoras is remembered especially for the following saying:

Man is the measure of all things: of the things that are, that they are, of the things that are not, that they are not.

Apparently not enough remained, to assess how far Protagoras and others went in purely philosophical skepticism. In general, anyway, unlike the later school of skeptics, the sophists were not inclined to immerse themselves in logical skeptical arguments. Instead, they preferred rhetoric over logic, and they taught young men how to use rhetoric for practical success, in private and public life.


As one answer has already pointed out the locus classicus of this is Parmenides.

He stated that what actually is, is unchangeable; this is in contrast to the world that we see, which as Aristotle noted is full of change (and he said science was the art of discerning the principles of change).

Its probably likely that this notion was not original with Parmenides, but he provided an extended argument supporting this thesis. (One might posit that mythically this arose with contemplating the sun as the source of all life on earth and thus all change on earth, yet in itself it is unchanged - but this is speculation).

Hence the idea arose that the world that we see is an illusion; that it is mere appearance, or seeming; that it shines (schein) forth (from a hidden lamp - being); or overflows - thus theories of real being that are emanatory theories (which includes modern cosmology - in a sense).

Similar ideas have arisen in Vedanta where the notion of the world being an illusion is called maya; and Buddhism where the real is altogether denied - it lacks svabhava (own-ground or real being).

However the word 'illusion' is a little strong, given the world that we see is manifestly real; I mean it is not the fantasy world of a fiction; thus in Buddhism they distinguish between conventional reality & ultimate reality - and this might be a better way to look at it.

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