Descartes: Doubt And Certainty

In his Meditations, Descartes chooses not to doubt the existence of God, the immortality of the soul, and the validity of his own existence.

Descartes' method of doubt

Descartes begins by laying out his reasons for doubting all his beliefs and the method by which he will go about doing it. He feels that he has been wrong so many times and is unsure why he believes certain things, so he resolves to build a new belief system on solid ground. To do this, he must first doubt all his previous beliefs.

The philosopher starts with his senses, which he can deceive. He acknowledges that his senses can be tricked, but only with respect to objects that are very small or far away. He then considers the possibility that he might be dreaming, but realises that even dreams are drawn from waking experiences.

Descartes then introduces the idea of a deceptive God, which he later changes to an evil demon. He supposes that this being has made him believe everything he knows is false. By doubting everything, he can ensure that he is not misled by the demon.

This method of doubt is not meant to be taken literally. It is a tool to help Descartes set aside preconceived opinions and find genuine first principles. It is an important part of his metaphysical inquiry, helping him redirect his attention from confused imagery to clear and distinct ideas of the intellect.

The dream argument

In his Meditations on First Philosophy, René Descartes introduces a method for rooting out his biases and establishing a secure foundation for knowledge. This method, known as the Cartesian Method of Doubt, involves inquiring after the foundations of beliefs in order to cast doubt upon them and, by extension, the entirety of one's belief system. The goal is to tear down all your beliefs in order to build up a new set of beliefs with a more justifiable foundation.

The Meditator reasons that he need only find some reason to doubt his present opinions in order to prompt him to seek sturdier foundations for his knowledge. He acknowledges that our senses are often fooled and that insane people might be more deceived, but that he is clearly not one of them. However, the Meditator realizes that he is often convinced when he is dreaming that he is sensing real objects. He feels certain that he is awake and sitting by the fire, but reflects that often he has dreamed this very sort of thing and been wholly convinced by it.

This is the basis of the dream argument, which states that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted. Therefore, any state that is dependent on our senses should be carefully examined and rigorously tested to determine whether it is in fact reality.

The Meditator acknowledges that even dream images are drawn from waking experience, much like paintings in that respect. Even when a painter creates an imaginary creature, like a mermaid, the composite parts are drawn from real things—women and fish, in the case of a mermaid. And even when a painter creates something entirely new, at least the colors in the painting are drawn from real experience. Thus, the Meditator concludes that, although he can doubt composite things, he cannot doubt the simple and universal parts from which they are constructed, like shape, quantity, size, time, etc. While we can doubt studies based on composite things, like medicine, astronomy, or physics, he concludes that we cannot doubt studies based on simple things, like arithmetic and geometry.

On further reflection, the Meditator realizes that even simple things can be doubted. An omnipotent God could make even our conception of mathematics false. One might argue that God is supremely good and would not lead him to believe falsely in all these things. But by this reasoning, we should think that God would not deceive him with regard to anything, and yet this is clearly not true. If we suppose there is no God, then there is an even greater likelihood of being deceived, since our imperfect senses would not have been created by a perfect being.

The deceiving God argument

In his Meditations on First Philosophy, Descartes introduces the idea of a deceiving God as a way to cast doubt on the reliability of human senses and even mathematics. He begins by acknowledging the existence of an all-powerful God who has created humans. Descartes then suggests that this God could deceive humans, making them believe false things even about mathematics, which is often considered to be a certain and reliable field of knowledge. This argument is known as the "deceiving God argument" and is a part of Descartes' broader method of systematic doubt, where he questions the validity of his beliefs.

• We believe in the existence of an all-powerful God who has created us.
• This God has the power to deceive us and make us believe false things.
• Therefore, we cannot be certain about our mathematical knowledge or our senses, as they may be deceiving us.

The implications of this argument are far-reaching. If an all-powerful God can deceive us, then all our knowledge, including what we perceive through our senses and even our understanding of mathematics, could be false. This radical skepticism challenges the foundation of human knowledge and raises questions about the nature of truth and certainty.

However, it is important to note that Descartes does not necessarily believe that God is deceiving us. Instead, he uses this argument as a thought experiment to explore the limits of human knowledge and the possibility of doubt. By considering the extreme scenario of a deceiving God, Descartes aims to establish a firm foundation for knowledge by identifying what cannot be doubted, even in the face of such deception.

In response to the deceiving God argument, Descartes introduces the concept of an "evil demon," which allows him to explore these ideas further without directly accusing God of deception. This shift from God to an evil demon was also strategically important, as openly questioning God's truthfulness during Descartes' time could have led to accusations of heresy.

By employing the deceiving God argument, Descartes laid the groundwork for his subsequent arguments and conclusions in the Meditations on First Philosophy. Through this method of systematic doubt, he aimed to rebuild the edifice of knowledge on firmer ground, seeking certainty in the midst of radical skepticism.

The evil demon argument

In the First Meditation, Descartes aims to determine which of his beliefs amount to knowledge. He argues that if there is any doubt regarding the truth of a proposition, one does not know that proposition. For example, Descartes reflects that although he may appear to know that he is sitting by the fire, the sensory experience of sitting by the fire could be an illusion or a dream. If a sensory experience could be caused by a dream, it is not certain and hence not knowledge.

To subject all beliefs to rigorous sceptical doubt, Descartes introduces the idea of an 'evil demon' or 'evil genius'. He reasons that a demon intent on deceiving him could easily make it appear that he is sitting by the fire, even if this was not the case. If Descartes' sensory experience of sitting by the fire could be caused by an evil demon, he does not know that he is sitting by the fire. Importantly, Descartes is not suggesting that such a demon exists—the mere possibility of the demon existing is enough to deprive him of knowledge. Since we cannot determine whether we are being deceived by an evil demon, we cannot rule out the evil demon possibility.

Descartes' argument can be structured as follows:

• I know a proposition only if I can rule out the possibility of it being false.
• If I am being deceived by an evil demon, then all propositions I believe are false.
• Therefore, in order to know a proposition, I need to rule out the evil demon possibility.
• I cannot rule out the evil deceiver possibility.
• Therefore, I lack knowledge.

Having established this strict criterion for knowledge as being immune from doubt, Descartes goes on to argue that knowledge of one's own existence does, in fact, meet this criterion. For Descartes, we do know that we exist. Knowledge of one's own existence escapes the sceptical conclusion because if I am being deceived, I must exist in order for there to be an 'I' which is deceived.

The evil demon is also mentioned at the beginning of the Second Meditation. Descartes says that if there is "a deceiver of supreme power and cunning who is deliberately and constantly deceiving me" then he himself must undoubtedly exist for the deceiver can "never bring it about that I am nothing so long as I think that I am something".

Some writers make no distinction between the deceiving God and evil demon arguments, regarding anything said about the former as being equivalent to the latter. Other writers acknowledge that Descartes makes mention of both but then claim they are 'epistemologically equivalent'. However, some insist that it is important to maintain the distinction between the two.

The cogito argument

In the Second Meditation, Descartes writes:

> I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I too do not exist? No: if I convinced myself of something then I certainly existed. But there is a deceiver of supreme power and cunning who is deliberately and constantly deceiving me. In that case I too undoubtedly exist, if he is deceiving me; and let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something. So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.

However, Descartes does not yet accept that he is a thinking mind inside a body. After all, the deceiver could have convinced him that his body and the physical world exist. He moves to another question: what is the "I" that is doing the thinking?

The answer is that the mind is a purely thinking thing. Descartes concedes, however, that though what he perceives with his senses may be false, he cannot deny that he perceives. So the human mind is capable of both thought and perception.

Another objection is that Descartes' argument is not an inference, but a non-inferential, performative utterance. Jaakko Hintikka, for example, argues that the transition from "I think" to "I am" is non-logical, and that the statement "I do not exist" is not logically incoherent.

Despite these objections, the Cogito Argument remains one of the most influential arguments in the history of philosophy, and a cornerstone of Descartes' philosophical system.

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