How does Descartes use the Watermark argument to prove the existence of the external world?
Answer by Martin Jenkins
The Watermark or ‘mark of the craftsman’ argument is employed by Descartes as one of his arguments or proofs for the existence of God, not directly to prove the existence of an external world per se. The existence of a good, benevolent God would guarantee the continuous and independent existence of a world beyond the senses.
Its import is that what is in the effects of an act, must be in the cause of that act. An argument which can find its origin in Aristotle’s Metaphysics. The influence of this approach can be found in later Cosmological proofs and Arguments from Design for the existence of a creator God.
Anyway, to the 3rd Meditation and we find Descartes, after establishing that he is an existing because thinking thing, is searching for anything else which can be discerned by ‘clear and distinct’ apprehension.
He has images of things and a world that exists beyond him. He has no control over such images and, he has been taught by nature that such a world exists — its common sense, so to speak. Yet the ‘teachings of nature’ have previously misled him so, they are not indubitable. Again, it is possible that such images are undistinguishable from dreams. So, no conclusive, indubitable conclusions about the existence of a world existing independently of him.
What of ‘Objective Ideas’ as so concluded by his Judgement about ‘the Wax’ (see the Second Meditation). These must have as much reality in their effects as in their causes, as from where else would such reality in the effects arise from? The cause powers the effects, for out of nothing comes nothing (ex nihilo nihil fit) so an effect must draw its reality from an existing or, prior existing cause. The examples of the stone and of heat follow.
In light of this, Descartes then considers considers the idea of God. God is infinite. Only what is infinite cause can create infinite effects. The creation of the infinite cannot proceed from what is less perfect, from which contains less reality — it cannot emerge from anything finite. This is clear and distinct reasoning.
Arguing that he has not obtained the idea of God by means of his sense-organs, nor is it a fiction or product of his mind, Descartes concludes that the idea is innate.
“Certainly I ought not to find it strange that God, in creating me, has placed this in me, to be as it were, the mark of the craftsman imprinted on his work.”
A thinking Descartes could not produce the reality of the idea of God, (finite, imperfect cannot produce the infinite, perfect) so this God must exist and must have put the idea of himself in Descartes along with, the ‘natural light’ of ‘clear and distinct’ thinking which evidences the Idea and nature of God. For God has made him in his image and similitude.
Examination by the reasoning Mind upon the nature of God, upon his perfect, ultimate nature -which is free from defects — further concludes:
“And from all this it is sufficiently evident that He cannot be a deceiver, it being manifest by the natural light that all fraud and deception proceed from defect.”
God cannot deceive. He has created the real, existing world of object that Descartes has questioned. Additionally, God has imbued Descartes and human beings generally with the faculty of reason (clear and distinct ideas) by which the truth of things can be concluded. Finally, God has created the order of Nature — including the human body. What Nature teaches can be taken to be created by God and be discerned by thinking beings as Natural Laws.
Baseer, I hope this helps.