笛卡尔之所以不从世界的存在或世界的某些特征入手证明，是因为目前（第三个沉思当时）还没有建立世界的存在性。相反，他从沉思者有上帝的观念这个事实入手，得出“仅有的事实是我存在，在我里面有一个关于最完满存在的观点，也就是关于上帝的观点，这就提供了一个非常清晰的论证，神的确存在。”（that the mere fact that I exist and have within me an idea of a most perfect being, that is, God, provides a very clear proof that God indeed exists.）他说，“神创造我，把这个观念放到我的心灵里，这没什么可惊奇的，这就像商人把商标放到他的产品里一样。”（it is no surprise that God, in creating me, should have placed this idea in me to be, as it were, the mark of the craftsman stamped on his work.）所以该论证被称作“商标论证”。
的确，给我表象实体的那些观念，无疑地比仅仅给我表象样式或偶性的那些观念更多一点什么东西，并且本身包括着（姑且这样说）更多的客观实在性，也就是说，通过表象而分享程度更大的存在或完满性。再说，我由之而体会到一个至高无上的、永恒的、无限的、不变的、全知的、全能的、他自己以外的一切事物的普遍创造者的上帝的那个观念，我说，无疑在他本身里比给我表象有限的实体的那些观念要有更多的客观实在性。
“Undoubtedly, the ideas which represent substances to me amount to something more and, so to speak, contain within themselves more objective reality than the ideas which merely represent modes or accidents. Again, the idea that gives me my understanding of a supreme God…certainly has in it more objective reality than the ideas that represent finite substances. Now it is manifest by the natural light that there must be at least as much reality in the efficient and total cause as in the effect of that cause. For where, I ask, could the effect get its reality from, if not from the cause? And how could the cause give it to the effect unless it possessed it? It follows from this both that something cannot arise from nothing, and also that what is more perfect—that is, contains in itself more reality—cannot arise from what is less perfect.”
Using the above ideas Descartes can claim that it is obvious that there must be at least as much reality in the cause as in the effect for if there wasn’t you would be getting something from nothing. He says “the idea of heat, or of a stone, cannot exist in me unless it is put there by some cause which contains at least as much reality as I conceive to be in the heat or in the stone. For although this cause does not transfer any of its actual or formal reality to my idea, it should not on that account be supposed that it must be less real.”
Since the idea of God contains the level of (objective) reality appropriate to an infinite substance it is legitimate to ask where an idea with this level of reality came from. After considering various options Descartes concludes that it must come from a substance that has at least the same level of (formal) reality. Therefore, an infinite substance, i.e. God, must exist.
Outline of Descartes' argument
My ideas may be innate, adventitious (i.e. come from outside me), or have been invented by me. As yet I don't know their true origin.
If ideas are considered simply as modes of thought, they are all equal and appear to come from within me; in so far as different ideas represent different things they differ widely. Ideas which represent substances contain within themselves more objective reality than the ideas which merely represent modes; the idea that gives me my understanding of a supreme God, (eternal, infinite, etc.) has more objective reality than the ideas that represent finite substances.
It is manifest by the natural light that there must be at least as much reality in the efficient and total cause as in the effect of that cause.
It follows from this both that something cannot arise from nothing, and also that what contains more reality cannot arise from what contains less reality. And this applies not only when considering formal reality, but also when considering objective reality.
Although the reality in my ideas is merely objective reality what ultimately causes those ideas must contain the same formal reality. Although one idea may originate from another, there cannot be an infinite regress here; eventually one must reach a primary idea, the cause of which will contain formally all the reality which is present only objectively in the idea.
Ideas are like pictures which can easily fall short of the perfection of the things from which they are taken, but which cannot contain anything greater or more perfect.
If the objective reality of any of my ideas turns out to be so great that I am sure the same reality does not reside in me, either formally or eminently (i.e. potentially), and hence that I myself cannot be its cause, it will necessarily follow that I am not alone in the world, but that some other thing which is the cause of this idea also exists.
In addition to being aware of myself, I have other ideas— of God, corporeal and inanimate things, angels, animals and other men like myself. Except for the idea of God, it doesn't seem impossible that these ideas originated from within myself.
By the word ‘God’ I understand a substance that is infinite, eternal, immutable, etc. These attributes are such that it doesn't seem possible for them to have originated from me alone. So from what has been said it must be concluded that God necessarily exists.
Further considerations:
Although I have the idea of substance in me by virtue of being a substance, this does not account for my having the idea of an infinite substance, when I am finite. This idea must have come from some substance which really was infinite.
I cannot have gained the idea of the infinite merely by negating the finite. On the contrary, to know that I am finite means knowing that I lack something and so must first have the idea of the infinite to make that comparison.
The perfections which I attribute to God do not exist in me potentially. It is true that I have many potentialities which are not yet actual but this irrelevant to the idea of God, which contains absolutely nothing that is potential. It might be thought that my gradual increase in knowledge could continue to infinity but firstly, this gradual increase in knowledge is itself a sign of imperfection and, secondly, God I take to be actually infinite, so that nothing can be added to his perfection whereas increasing knowledge will never reach the point where it is not capable of a further increase. Finally, the objective being of an idea cannot be produced merely by potential being, which strictly speaking is nothing, but only by actual or formal being.
Additional argument for the existence of God:
I couldn't exist as the kind of thing that has this idea of God if God didn't exist, for I didn't create myself, I haven't always existed, and, although there may be a series of causes that led to my existence, the ultimate cause must be such that it could give me the idea of God and this, for the reasons already given, will be God.
This idea of God didn't come to me via the senses, nor did I invent this idea for I am plainly unable either to take away anything from it or to add anything to it. The only remaining alternative is that it is innate in me.
Criticisms of the trademark argument
Cunning notes that “Commentators have argued that there is not much hope for the argument from objective reality.”[7]:112 Wilson says that she will say little about Descartes arguments for the existence of God for “while these arguments are interesting enough, I don’t think Descartes is in a position to defend their soundness very forcefully.”[8]:100 Williams comments that “Descartes took these hopeless arguments for the existence of God to be self-evidently valid, conditioned in this by historical and perhaps also by temperamental factors.”[1]:196
Hobbes' complaint that Descartes hasn't offered an adequate account of degrees of reality doesn't seem to have been answered and Descartes’ response that it is ‘self-evident’ surely isn't enough. There may be some superficial appeal in the claim that an actual flower has more reality than an idea of a flower but this needs to be unpacked. ‘Reality’ cannot be equated with ‘existence’ for, apart from the fact that ‘degrees of existence’ is hardly less problematic than ‘degrees of reality’, as Wilson comments, “reality must not be confused with existence: otherwise the existence of God would be overtly assumed in the premises of the argument.”[8]:137
Even if the argument is judged on its own terms and we grant that there can be degrees of formal reality and degrees of objective reality there are still significant problems. Crucial to the argument as it is normally reconstructed is that the degree of objective reality is determined by the degree of formal reality that the thing being thought about would have if it existed. Descartes offers no reason why this should be so. Wilson says, “Descartes has simply made an arbitrary stipulation here.”[8]:137 There seems to be no good reason why we couldn't maintain different degrees of objective reality but insist that the idea of an infinite substance still has less reality than the amount of reality conferred by the formal reality of a finite substance.
Descartes may be inconsistent on this point for in the Replies he says of objective existence, “this mode of being is of course much less perfect than that possessed by things which exist outside the intellect; but, as I did explain, it is not therefore simply nothing.”[2]:75 Despite what Descartes appears to say in the Meditations it may be necessary for the objective reality to be less than the formal reality of the thing represented. Williams points out, “God, as the argument insists, has more reality or perfection than anything else whatever. Hence if Descartes’s idea of God is not itself God (which would of course be absurd), it cannot, however regarded, possess as much reality as God, and hence cannot demand as much reality in its cause as God possesses. So the argument seems to fall short of positing God as cause of the idea.”[1]:128 He goes on to say that Descartes must, therefore be relying on something more than the general principle that there must be as much formal reality in the cause of an idea as there is objective reality in the idea itself. Instead, he suggests, Descartes is relying on special features of the idea of God: “the infinity and perfection of God, represented in his idea, are of such a special character, so far in excess of any other possible cause, that the only thing adequate to produce an idea of that would be the thing itself, God.”[1]:128
Then there is the problem of how it can be possible for a finite mind to have a clear and distinct idea of an infinite God. Descartes was challenged on this and in the first set of Replies says, “the infinite, qua infinite, can in no way be grasped. But it can still be understood, in so far as we can clearly and distinctly understand that something is such that no limitations can be found in it, and this amounts to understanding clearly that it is infinite.”[2]:81 Cottingham argues that making this distinction is “an unsatisfactory line of defence”[6]:129 He refers to Descartes own analogy of a man who had an idea of a very complex machine from which it could be inferred that he had either seen the machine, been told about the machine or was clever enough to invent it.[9]:198 He adds, “But clearly such inferences will hold only if the man has a quite determinate idea of the machine. If a man comes up and says that he has an idea of a marvellous machine which will feed the hungry by making proteins out of sand, I shall be impressed neither by his experience nor by his powers of invention if it turns out that that is all there is to the idea, and he has no conception, or only the haziest conception, of how such a machine might work.”[6]:129
Finally, it might be added, for this proof to do the work Descartes is asking of it the proof needs to be clear and distinct. Given the above considerations this is unconvincing. In the second set of replies Descartes says this is the fault of the reader:
“I do not see what I can add to make it any clearer that the idea in question could not be present to my mind unless a supreme being existed. I can only say that it depends on the reader: if he attends carefully to what I have written he should be able to free himself from the preconceived opinions which may be eclipsing his natural light, and to accustom himself to believing in the primary notions, which are as evident and true as anything can be, in preference to opinions which are obscure and false, albeit fixed in the mind by long habit… I cannot force this truth on my readers if they are lazy, since it depends solely on their exercising their own powers of thought.”[2]:97
^ 8.08.18.2Wilson, Margaret. Descartes. Bombay: Popular Prakashan Private Ltd. 1960.
^Cottingham, John; Stoothoff, Robert; Murdoch, Dugald. The philosophical writings of Descartes vol1. Cambridge: Cambridge University Press. 1985. ISBN 0-521-63712-0.
Sources
René Descartes, Meditations and Other Metaphysical Writings
Christopher Hamilton (2003), Understanding Philosophy
