Is Descartes' argument in the Third Meditation for the existence of God sound?

At this point it is necessary to clarify that Descartes believes that ideas have a representational content (i.e. they represent something in the real world) and calls this, the idea’s ‘objective reality’. Thirdly, Descartes applies the Causal Adequacy Principle to ideas, to the features that are part of the representative content of an idea. In the same way that the inventor of a machine has the concept of it in his mind (i.e. as an idea) and in the material world, it is just as adequate to say that the cause of the machine in the physical world is the inventor’s idea as it is appropriate to ask what the cause of the idea is. For that too must be contained in its cause, whatever that may be. 

Lastly because the meditator has the idea of God as a perfect being, then the cause of this idea must be something that contains in itself all the features found representatively in the idea. The meditator is not the cause of this idea because he is a finite being, therefore imperfect. Because ‘there cannot be an infinite regress of causes’ there must be a ‘primary idea’ which contains the perfection that is merely representatively present in the idea. Descartes believes ‘there is more reality in an infinite substance than in a finite one…for how could I understand that I…was not wholly perfect, unless there were in me some idea of a more perfect being which enabled me to recognise my own defects by comparison’. As a result of this line of thinking God necessarily exists according to Descartes, for in sum the cause of the meditator’s idea of a perfect being must be something that possesses these perfections. This is God.

The argument seems to stress that an effect, here the idea, possesses properties belonging to its cause. However if we consider the example of a sponge cake, which is made up of egg, flour, butter etc, we find that the property of sponginess does not apply to the cause (i.e. the ingredients) as it does to the effect. Although this sponginess does not appear out of a vacuum, but by the chemical reactions involved, this analogy does not support Descartes conclusion. However, it can be said that the ingredients potentially contain sponginess. Although it may at this appear that the argument fails, Descartes defends himself by saying his argument requires the cause of the idea of God to be something that is actually perfect and not potentially.

This same line of criticism is more significant when speaking of an ‘efficient’ cause rather than a ‘material’ cause. For example, if the efficient cause of life is sun and rain, then living animals have arisen from non-living causes thus it appears that there is no relationship between the cause and the effect. Descartes provides a two-fold reply. Firstly he says animals do not have any perfections which are present in non-living things. Secondly, the Causal Adequacy Principle stresses the total cause of an effect in addition to the efficient cause. In other words because animals possess perfections that are not found in the rain and sun, it is evident for Descartes that these things cannot be the total causes of living things.

However by making such a reply Descartes opens himself to attack from those who support the Darwinian theory of Evolution, under which living things can evolve from non-living things. This is a controversial topic in its own right and shall not be discussed in further depth in the course of this essay.

Descartes has been criticised for applying the Causal Adequacy Principle to ideas. In the First Set of Objections, the critic says that because an idea is subjective it does not require a cause. Descartes replies that because ideas do not exist in the material world it does not entail that they do not require a cause. It seems this reply is adequate on the grounds of his explanation about an inventor outlined previously. 

In has been the natural case that critics have responded by saying that the idea of God need not necessarily been the cause of God, but instead of social development. This is easy for Descartes to deal with for he can just say that if we regress further enough we will find the cause of this social development, and so forth until we arrive at the primary cause. ‘Somewhere down the line we will have to suppose a being of sufficient perfection to account for the perfection represented in the idea’.

Some critics have suggested that we do not have an idea of God (see Third Set of Objections). Descartes replies that the very fact that we understand what is meant by the infinite perfections of God shows we do have an idea of God. Furthermore Descartes adds that it is possible to understand something even though it is difficult to believe. It is difficult not to agree with Descartes here, for we do understand what ‘God’ means, irrespective of belief or disbelief. However the question remains as to why this being has to be infinite rather than finite. Descartes replies in the Ninth Objection raised in the Third Set of Objections that the infinite takes priority over the finite, for ‘if there is an infinite and independent substance, it is more of a thing than a finite and dependent substance’. In his objection Frans Burman says it is illogical to say that the meditator arrives at his imperfection before he arrives at knowledge of God.  To this Descartes replies that irrespective of the order it is discovered the infinite nature of God comes before our finite nature because imperfection is a mirror image of God’s perfection. Despite his efforts, it is apparent that Descartes argument for the existence of God presented in Meditation III is not sound because it is just as necessary to know what finite is to understand what infinite is, just as much as it is necessary to know what infinite is to understand what finite is. There is no ranking element to be considered.

Towards the end of the Third Meditation Descartes introduces another line of reasoning about the existence of God. This time he starts from the idea of God as a perfect being. Descartes asks if I have the idea of God but no such being actually existed is it possible for me to exist? His answer is no because it implies that he is self-creating or the result of an infinite regress of causes. This results in absurdities for Descartes, as to be self-creating implies that one would give themselves all the perfections, but this is clearly not the case.

This chain of thought is dependent on the first, which we have already seen has its problems. Primarily, it depends on accepting the Causal Adequacy Principle and that this principle can be applied to ideas. Therefore it makes it difficult for it to carry any real weight.

Some critics have seen parallels between Descartes argument for the existence of God and the Cosmological Argument proposed by Aquinas: the argument that there is evidence of a series of causes in the world therefore there must be an uncaused cause. Aquinas’ argument was not sound because it was dependent on a premise dependent on ambiguous sensorial experience. However, Descartes immediately dispels the parallel drawn by outlining that his initial premise is not that there are causes in the world, since this would be dependent on doubtable sensorial experience.  

In conclusion, if we refer to our original definition of a philosophically sound argument we find that although Descartes conclusion may be correct there still remains the possibility of holding an opposing view simply on the grounds that the world may just be a ‘brute fact’ as John Hick calls it. If so there appears no need to infer God’s existence.