Even though this isn't exactly accurate, the way I like to think of Descartes' hyperbolic doubt as stating that there's no way to prove that information gained through sensory experience is accurate. After all, in a dream, the dreamer fully believes that his experiences are 'real', but they are not, which he only discovers in retrospect.

I wonder, however, how deeply this is tied to a much less popular (today, that is) belief of Descartes, that the functions of the mind are mainly the products of an immaterial soul which relates to the body but is independent of it. If the mind is materialistic, and even Descartes believed that his own mind must exist ('mind' being defined as merely a consciously thinking thing) then does it necessarily follow that that the mind receives chemical signals from a body, which have sense organs stimulated by an external world, etc. and thus get out of Cartesian (or hyperbolic) doubt?

I've also heard that Descartes' doubt could be solved by appealing to evolution: in order to survive, wouldn't the mind need to correctly perceive its surroundings?

(Please see my own answer before posting a different one)

2 Answers 2


I believe that the answer is no, for several reasons (ordered weakest to strongest):

  1. As Descartes himself noted, part of the argument is based on the existence (and therefore possibility) of a dream-state. Even the materialist cannot argue that the mind is capable of being fooled, by anything from optical illusions to dreams, and that whatever chemical signals are necessary for brain states, these chemical signals clearly don't require outside stimuli that correspond perfectly to the mind's perception of them.

  2. Even by appealing to evolution fails in an attempt to show that the mind necessarily perceives its environment correctly, and that a dream-state or similar reality-misrepresentation-state cannot be the mind's permanent state. One proposing to relieve Descartes of his doubt might say, "well, since the brain evolved by surviving, which depends on correct representation of the outside universe - the only way for a body-mind to get away from a bear or similar danger, is for it to be able to see the bear, and see a heavy stone to hit it with, etc." However, this isn't necessarily true - perhaps instead of the bear that the mind perceived, reality was that an object of a different nature were in front of this mind-body, and the only way to continue surviving would be to move towards this object. However, the mind-body evolved to perceive a bear and to think that it's acting in a particular manner, when in actuality it's acting in the opposite manner - but this is all beneficial to the mind-body, because the end result is that it does the action that allows its survival. Hence, evolution cannot help Descartes out of his doubt.

  3. The only reason to believe in materialism (or evolution, or anything for that matter) is to believe in the scientific findings/theories etc, which are based in turn on sensory observations. There's no reason to justify a materialistic conception of the mind-body problem, unless one already believes in the existence of a material environment.


Descartes solved his doubt himself and proved the primacy of the mind over the body with his "cogito ergo sum".

  • the question is specifically directed at materialists; that's the whole point (see title: 'depend on Cartesian dualism')
    – That Guy
    Jul 3, 2014 at 3:01
  • descartes argument negates materialism, that's the point, therefore the answer is no, in agreement with your own answer of no, it does not depend on his dualism. i dont believe i missed the point and merely elaborated on the point that you missed. Jul 4, 2014 at 4:24
  • Oh! I didn't get it the first time, sorry. Do you mind clarifying that a bit in the answer, please? If I understood correctly, you're saying that Descartes' dualism depends on his 'cogito ergo sum', and not the other way around, right? I didn't read it (Meditations) that way but it makes sense
    – That Guy
    Jul 4, 2014 at 4:36

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