Is Descartes
successful in proving the external world?
Descartes tend to be categorised a rationalist, but this is a simplification, both of his approach and his motives. On one level, his work can be seen as that of a man trying to reconcile science and belief. He writes always of foundationalist beginnings, upon which he can base a more coherentist framework of �scientia�. But there is not really a simple dichotomy: rather the conflict is apparent between the practical, empiricist, experimental leanings of his scientific mind with the religious, ideal intellectualism in which he was brought up and believed. Seen in this way, the aim of the Meditations is two-fold: providing a metaphsyical grounding which will justify and hopefully further the progress of human rational and scientific endeavour; and proving God�s existence and lifting humanity above the animals by our souls and reason. Like Newton after him, practicing science is almost doing God�s work, by employing our divine sovereign reason fruitfully.
When we talk of his proof of the external world being �successful�, we might ideally like him to provide a conception of reality objective enough to explain ourselves, animals and inanimate objects, thought and the mind-body interaction and our perception of secondary qualities; in his own terms though, success would be measured largely in providing grounds for certainty in science, but a science explicable in divine terms.
Garber demonstrates that Descartes develops two alternate routes in trying to climb outside his own mind and perceptions to explain the local and subjective in terms of the more objective.
In his early unfinished Rules, Descartes describes a method of scientific enquiry where a problem is reduced to a more and more basic level until an explanation for a fundamental question can be intuited. From there, the Enquirer/Scientist can deduce downwards, through intuition of the validity of the inferences connecting the propositions, to the original issue. In many ways this is a more satisfying explanatino of method than the free-floating forward method of the Meditations, because it sketches out the path as well.
Garber uses the examples of the rainbow and the anaclastic line to demonstrate the two-stage reduction then deductive construction. Since they both involve the physics of optics, they are both grounded on the intuition of light as a �natural power�. However, experimentation has been necessary to limit the avenue of enquiry and to better understand and define the question being asked. This is an admission that the external world is sometimes accessible only on in its own terms. The theory then formed is rational and grounded on intuition; the theory verifies the observations from which it is conceived. Garber goes on to try and show that this is blend of rationalism and empiricism is not paradoxical, though that is not our concern here. The point is to contrast this means of establishing scientia by grounding everything on the intuitable, with that of the Meditations, which dives in at the first principles and tries to convulutedly ratify a ready-made external world and truth criterion in one go.
In major respects, the approach outlined in the Rules is akin to the Meditations, because it too appears to take a foundationalist view of knowledge, simply approaching it from a bottom-up rather than top-down direction. Both approaches rely on intuited starting premises as forming the base of the epistemic structure, with intuited inferences to build up towards a scientific picture. In order for the method of the Rules to be complete in its scope, there have to be levels beyond what is intuited, so that the Enquirer/Scientist can extend his enquiry all the way back towards first principles. Then, the Meditations could be constructed in reverse but upon the same foundations. However, this approach could have unforeseen consequences � if any intuition were to depend on any other aspect of knowledge, Descartes could be trapped in a coherentist structure, which may or may not allow him to rest everything on his foundations of God and the Cogito. He also treads a dangerous line with his use of experiment, when linking the phenomena back to its ultimate intuition; he gives an example of how knowledge of other natural powers may be necessary in deducing downwards about light, hinting at the need for some knowledge about the external world already may be necessary in drawing the analogy. So the Rules is useful perhaps for a scientist already confident about first principles � to use it in the same way that Descartes uses the Meditations would be to re-trace the same path in reverse. But this might not even be possible, since the path of the Meditations is necessarily a circuitous spiral, while the Rules forms a perfect pyramidal structure � the Cartesian circle might prove even more awkward to resolve.
In writing the Meditations, Descartes can be seen then as recognising that there will always be an underlying unanswerable �but why is it like that?� The intuition �light is a natural power� is not a bottom-line. Thus Descartes� second route to proving the external world is to start from the foundations: a relatively easy intuition of consciousness, from which he over-extends wrongly: from �I am thinking, therefore I exist� to �I am a thinking thing�, from thoughts to mind. Then he attempts to prove God, a non-deceiving God who can provide his clear and distinct perceptions with a guarantee of truth, and then the external world is no longer completely disjointed from the subjective perceptions.
The discussion of the external world first requires Descartes to describe his conception of it, not in perceptual terms, but in intellectual terms. This is necessary in order for such clear and distinct perceptions to be validated by God � but crucially, it is his conception not an internal image which is perceived clearly and distinctly. I will discuss this description, then the terms of the proof in turn.
When Descartes concludes that he �perceives [the wax] with his understanding�, he means that:
� he has a conception of matter as that which is extended and goes through changes of shape and position and in which we perceive secondary qualities to be manifested;
� he has a conception of wax in general as matter which is perceived as having the secondary qualities of wax;
� and he has a conception of this particular lump of wax as discernible, but shifting, bounded extension, and which is perceived as currently having the secondary qualities of wax
He comes to this clear and distinct conception of the wax�s essence having dissociated it from the various ephemeral sensory ideas with which we assume unthinkingly that we know the world. The senses can tell us nothing about corporeal essence, since they change, while by definition a substance�s essence is immutable. The essence of the phsyical world as extension must be grasped by the intellect not the imagination or the senses, because a clear and distinct perception of it requires abstraction from, rather than production of, a malleable multitude (or even infinitude) of altered images. This conception shows the essence of matter to be directly opposite to that of mind, i.e. pure divisible extension. The secondary qualities we associate usually with matter, e.g. colour, taste and texture, are less quantifiable, explanatory and objective than the primary quality, extension, of which they are effectively subjective illusions.
However, there are considerable problems accepting this, even if the argument behind it were solid � in fact, these objections could almost be seen as an reductio ad absurdium attack on Descartes� conception of matter.
� there can�t be science without experiment, and our experimentation hinges on secondary qualities
� how can objects increase or decrease in size? if we accept Descartes� description of their parts being more concentrated or rarefied, doesn�t that somehow require a void between the parts for them to slide into and away from each other, since they axiomatically cannot occupy the same space
� what forms the boundaries between different types/natures of objects? if we drop a lump of cold wax into milk, the two remain separate, conceptually and perceptually � but if we heat the milk enough for the wax to melt, so that the two mingle (but not react), then have the boundaries disappeared? what makes them different since they effectively share the same extension? if their essence is solely extension, how can they have different properties from each other?
� how can non-extensible phenomena such as light, fire, gas and wind be explained?
� is it in any way reconcilable with modern atomic explanations, or quantum mechanics?
So we find ourselves alking around our more objective conception of reality � it�s a barren, colourless world, like monocrhome blobs in a lava lamp, endlessly prowling within the boundaries of our primary-quality-only plenum. When we abandon the colours nad textures of our local representation of reality, this is what is left � simply a four-dimensional space-time continuum.
Descartes proof of the external world can be encapsulated as follows:
1. I have a clear and distinct perception, or at least I cannot see why it should not be, that there is an external world which actively causes the passive sense-perceptions I have
2. God is not a deceiver, which he would be if he were to cause or allow that something were not the case, though I had no rational means of perceiving so
3. there is an external world which resembles my conception, but not my perception, of it
Both the first and second steps raise certain issues. Is his clear and distinct perception of the wax as clear and distinct as the Cogito, for instance? Is he not stressing instead that he has no clear and distinct perception of why there shouldn�t be an external world? We will return to this as part of God�s guarantee below.
It seems as though God�s guarantee is being strained slightly here.
� is God deceiving us by presenting secondary qualities as seeming so real?
� just because they are involuntary does not necessarily prove an external source (without assuming the doctrine of perfect transparency of mind) � after all, as Descartes acknowledges, dreams are a product of one�s own mind
� Descartes has retreated to the �asylum of ignorance� in other instances � how can God be wholly inscrutable sometimes, and yet be guaranteed not to have a reason not to deceive us on other occasions
� is there any reason that the active cause of our perceptions might be external, but of mental rather than physical substance? after all, Berkeley based his system of the world existing as an idea in the mind of God on similar premises to Descartes, minus the substantive dualism
� God has at the very least �allowed� us to be misled, if not systematically, then at least in the particulars in various other instances. To say that he is self-imposing restrictions by working within a rules-based physical system, like nature, does not allay our fears. The fact remains that the dropsical man is misled by his own nature, despite his best attempts.
In conclusion, Descartes� proof of the external world in the Meditations holds insofar as you accept the cogence of the arguments and proofs presented before then. That is to say that he has proved the existence of an external world of some sort, one bereft of secondary qualities and characterised only by extension. On inspection, he has really proved little more than the existence of matter, i.e. that there are bodies of a corporeal nature which are the active external cause of his sense-perceptions. But this description does not leave it open that there is more to the external world � matter is extension, nothing more or different. Though it appears to have been proven, this description of the external world is an impoverished, unintelligble one to us � and as Williams argues, an absolute conception of reality, were it attainable, might be less informative than an objective, comprehensible one. With his self-defeating acknowledgement that this external world need not, and does not, closely resemble our mental representation of it, Descartes undermines our scientific body of knowledge, which rests on experiments on secondary qualities.