商標論證（英語：trademark argument）是法國哲學家兼數學家笛卡爾為了證明上帝的存在性做出的先驗論證。

在沉思集當中，笛卡爾為證明上帝的存在提供了兩個論證。第五個沉思（Meditation V）里，他做出本體論版本的證明，試圖從神的本性中推理上帝的存在；第三個沉思（Meditation III）里，他通過上帝行動（activity）的結果之一，呈現了這個存在性證明。商標論證即出自第三個沉思。

笛卡爾之所以不從世界的存在或世界的某些特徵入手證明，是因為目前（第三個沉思當時）還沒有建立世界的存在性。相反，他從沉思者有上帝的觀念這個事實入手，得出「僅有的事實是我存在，在我裡面有一個關於最完滿存在的觀點，也就是關於上帝的觀點，這就提供了一個非常清晰的論證，神的確存在。」（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.）他說，「神創造我，把這個觀念放到我的心靈里，這沒什麼可驚奇的，這就像商人把商標放到他的產品里一樣。」（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.）所以該論證被稱作「商標論證」。



潛在假設

要理解笛卡爾的論證，有必要理解笛卡爾使用的一些形而上的假設。

實在性等級

笛卡爾說道：

> 的確，給我表象實體的那些觀念，無疑地比僅僅給我表象樣式或偶性的那些觀念更多一點什麼東西，並且本身包括著（姑且這樣說）更多的客觀實在性，也就是說，通過表象而分享程度更大的存在或完滿性。再說，我由之而體會到一個至高無上的、永恆的、無限的、不變的、全知的、全能的、他自己以外的一切事物的普遍創造者的上帝的那個觀念，我說，無疑在他本身里比給我表象有限的實體的那些觀念要有更多的客觀實在性。
> 「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.」
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笛卡爾繼續把上面這段描述為「顯然正確」。評論者威廉說，「這是一段經院哲學的形上學，這也是笛卡爾的思想與我們之間，歷史鴻溝的醒目標誌之一，儘管當代現實中有很多他寫的其他東西。只有那個時代的人，才可以毫不猶豫地接受這個反直覺的純粹的、難懂的原則，認為這個原則在自然之光中（理性中）是自明的。」

在他的時代，霍布斯反對道，「此外，笛卡爾應當重新考慮什麼叫做『更多的實在性』。實在性允許自己更多或更少了嗎？還是笛卡爾自己認為一物可以比另一物更多地是一樣事物？如果是後者，我建議他考慮一下，他如何以每次證明都需要的清晰程度向我們解釋這一點，而他本人也曾在其他地方使用過這種證明。」

笛卡爾回復道：

「我已經…… 把實在性如何允許更多或更少，展示得很清楚了。實體比樣式更多地是一樣東西；如果有真的特質或不完全的實體，他們相比樣式就更大程度上是一樣東西，但相比完滿的實體就更不是一樣東西。最終，如果有無限的和獨立的實體，那它就比有限的和依賴的實體更是一樣東西。這些完全都是自明的。」

要想理解笛卡爾的商標論證，不必要完全理解潛在的亞里斯多德主義經院哲學的形上學，但有必要了解：


* 無限的實體有最多的實在性，多於：

* 有限的實體，而它的實在性又多於：

* 樣式。

實體是指獨立存在的東西（exist independently）。 真正獨立存在的是無限的實體，因為它不依賴任何其他東西而存在。在這個語境下，「無限的實體」就是指「上帝」。有限的實體要能獨立存在，必須依賴無限的實體。「實體」不一定是物理實體，對笛卡爾來說，物體是一種實體，心靈是另一種實體。

樣式（英語：mode）的詞典定義是「一種方式，於之某物發生，或被經驗、被表達或被完成。」 在這個定義下，實體（例如心靈）將有屬性（例如思想），樣式就可以是願意，或有觀點等等。

實在性的程度，與 某樣東西依賴於其他東西的 方法關聯 ——「樣式邏輯上依賴實體，他們『本質是主體』…… 被（上帝）創造的實體邏輯上不是，但因果上是，依賴於上帝的。他們本質上不是主體，但是卻是上帝作為造物主的結果。」

為了避免混淆，有必要注意，實在性的程度與其大小並不相關。相關的僅僅是一樣東西是怎麼依賴其他東西的而已。有人可能會誤解，被吹大的氣球，其實在性並不大於網球；森林的火，其實在性並不大於蠟燭的火苗。這兩個例子，想法都是錯誤的。

形式的實在性和客觀的實在性

注意，這裡的客觀實在性並不是日常意義上的客觀性，或客觀實在性。

笛卡爾說道，

> 觀念的本性是，對於其自身，它除了由我思產生外不需要任何形式的實在性，即它是我思維的樣式。但是對於給定一個觀念，為了維持這樣的形式的實在性和這樣的客觀的實在性，這個觀念必須由某些原因產生，這些原因里至少有，與觀念里客觀的實在性相等的，形式的實在性。
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「形式的實在性」可以粗略地理解為「實際存在」。 「客觀的實在性」並不是與主觀相反意義上的客觀，而更像是一個人思想里的對象，而不考慮這個對象現實中存不存在。 Cottingham 說，「客觀的實在性」是「一個觀念的表象內容」。 哈特費爾德說，「想像一個欲望著的對象，比如『你支持的球隊獲勝了』，這個欲望的對象現在可能並不存在，但也不需要它存在過。用笛卡爾的術語，「客觀的實在性」就是某些包含在一個人的心理狀態里的東西，因而用我們現在的話說可以是『主觀的』「。

對於笛卡爾的論證來說，至關重要的，是客觀的實在性其程度是怎樣被決定的。客觀的實在性的程度由形式的實在性決定，當然，這個形式的實在性是屬於被呈現或被思考的東西的。所以，我所有的觀念都有最低程度的形式的實在性，因為每個觀念都是樣式，但觀念里的無限實體，相比觀念里的有限實體，則有更多的客觀的實在性 Kenny 提醒道，「我們有時候用『實在性』（reality，現實）去與虛幻小說做區分；這樣看來，獅子的觀念會比獨角獸的觀念有更多的客觀實在性，因為前者存在而後者不存在。但這不是笛卡爾的本意。」 在這個例子裡，獅子的觀念和獨角獸的觀念，二者的客觀的實在性是相等的，因為獅子和獨角獸都是有限實體。



Applying the causal adequacy principle

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.」 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.」 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.」

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.」

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.」 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.」 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.」 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.」

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.」 Cottingham argues that making this distinction is 「an unsatisfactory line of defence」 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. 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.」

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.」
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參見


* Cartesian Circle



參考資料



Sources


* René Descartes, _Meditations and Other Metaphysical Writings_

* Christopher Hamilton (2003), _Understanding Philosophy_