商标论证
商标论证（）是法国哲学家兼数学家笛卡尔为了证明上帝的存在性做出的先验论证。
在沉思集当中，笛卡尔为证明上帝的存在提供了两个论证。第五个沉思（Meditation V）里，他做出本体论版本的证明，试图从神的本性中推理上帝的存在；第三个沉思（Meditation III）里，他通过上帝行动（activity）的结果之一，呈现了这个存在性证明。商标论证即出自第三个沉思。
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”。
要理解笛卡尔的论证，有必要理解笛卡尔使用的一些形而上的假设。
笛卡尔说道：
笛卡尔继续把上面这段描述为“显然正确”。评论者威廉说，“这是一段经院哲学的形而上学，这也是笛卡尔的思想与我们之间，历史鸿沟的醒目标志之一，尽管当代现实中有很多他写的其他东西。只有那个时代的人，才可以毫不犹豫地接受这个反直觉的纯粹的、难懂的原则，认为这个原则在自然之光中（理性中）是自明的。”
在他的时代，霍布斯反对道，“此外，笛卡尔应当重新考虑什么叫做‘更多的实在性’。实在性允许自己更多或更少了吗？还是笛卡尔自己认为一物可以比另一物更多地是一样事物？如果是后者，我建议他考虑一下，他如何以每次证明都需要的清晰程度向我们解释这一点，而他本人也曾在其他地方使用过这种证明。”
笛卡尔回复道：
“我已经……把实在性如何允许更多或更少，展示得很清楚了。实体比样式更多地是一样东西；如果有真的特质或不完全的实体，他们相比样式就更大程度上是一样东西，但相比完满的实体就更不是一样东西。最终，如果有无限的和独立的实体，那它就比有限的和依赖的实体更是一样东西。这些完全都是自明的。”
要想理解笛卡尔的商标论证，不必要完全理解潜在的亚里士多德主义经院哲学的形而上学，但有必要了解： 实体是指独立存在的东西（exist independently）。 真正独立存在的是无限的实体，因为它不依赖任何其他东西而存在。在这个语境下，“无限的实体”就是指“上帝”。有限的实体要能独立存在，必须依赖无限的实体。“实体”不一定是物理实体，对笛卡尔来说，物体是一种实体，心灵是另一种实体。
样式（）的词典定义是“一种方式，于之某物发生，或被经验、被表达或被完成。” 在这个定义下，实体（例如心灵）将有属性（例如思想），样式就可以是愿意，或有观点等等。
实在性的程度，与 某样东西依赖于其他东西的 方法关联——“样式逻辑上依赖实体，他们‘本质是主体’……被（上帝）创造的实体逻辑上不是，但因果上是，依赖于上帝的。他们本质上不是主体，但是却是上帝作为造物主的结果。”
为了避免混淆，有必要注意，实在性的程度与其大小并不相关。相关的仅仅是一样东西是怎么依赖其他东西的而已。有人可能会误解，被吹大的气球，其实在性并不大于网球；森林的火，其实在性并不大于蜡烛的火苗。这两个例子，想法都是错误的。
注意，这里的客观实在性并不是日常意义上的客观性，或客观实在性。
笛卡尔说道，
“形式的实在性”可以粗略地理解为“实际存在”。 “客观的实在性”并不是与主观相反意义上的客观，而更像是一个人思想里的对象，而不考虑这个对象现实中存不存在。 Cottingham说，“客观的实在性”是“一个观念的表象内容”。 哈特费尔德说，“想象一个欲望着的对象，比如‘你支持的球队获胜了’，这个欲望的对象现在可能并不存在，但也不需要它存在过。用笛卡尔的术语，“客观的实在性”就是某些包含在一个人的心理状态里的东西，因而用我们现在的话说可以是‘主观的’“。
对于笛卡尔的论证来说，至关重要的，是客观的实在性其程度是怎样被决定的。客观的实在性的程度由形式的实在性决定，当然，这个形式的实在性是属于被呈现或被思考的东西的。所以，我所有的观念都有最低程度的形式的实在性，因为每个观念都是样式，但观念里的无限实体，相比观念里的有限实体，则有更多的客观的实在性 Kenny提醒道，“我们有时候用‘实在性’（reality，现实）去与虚幻小说做区分；这样看来，狮子的观念会比独角兽的观念有更多的客观实在性，因为前者存在而后者不存在。但这不是笛卡尔的本意。” 在这个例子里，狮子的观念和独角兽的观念，二者的客观的实在性是相等的，因为狮子和独角兽都是有限实体。
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.Further considerations:Additional argument for the existence of God: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: