Descartes, in Meditations, establishes his mind, God and the external world through a priori intuition and demonstration. He starts off by using scepticism (philosophical doubt) as a tool. He doubts everything, both physical and metaphysical; he does this in order to get to a foundation for knowledge. He goes through three stages of doubt, the first being “Sense doubt” – he points to examples of optical illusions (a modern example would be Wittgenstein’s rabbit) and instances where his mind has deceived him. He thus concludes that his senses deceive him and can not trust information they give him. His second stage of doubt is known as “Dream doubt” in which he says that because we can not distinguish between dreams and the real world – who are we to say that what we are experiencing at this moment in time isn’t a dream? The first two stages have launched an attack on a posteriori knowledge not a priori; however his third stage attacks both. Known as “Demon doubt” and can be equated to ‘The Matrix’, Descartes says that everything we could see and understand could be placed there by a demon, including axiomatic and analytic statements. Despite all this mention of doubt, Descartes manages to be sure of one thing, his mind. Even if a demon was trying to make him doubt his mind, it would only prove the point that he has a mind! In fact, even if he tries to doubt his own mind, he has already established it because he is using it in the process. Descartes has proved his mind through pure reason, using his rational insight and thinking about it, he has deduced and intuited that this must be the case.
Now that Descartes has a foundation, he can infer other things. He goes on to prove that the mind can exist without the body. The body is sensed through experience, and yet, he has proven that this type of knowledge is deceiving. However his mind does exist, thus he concludes that the mind can exist independently of the body. By simply considering and intuiting, he sees that it must be the case, Descartes has established truths about what exist (through a priori intuition and demonstration).
Descartes then proves the existence of God through an a priori argument called the “Ontological argument”, it can be stated thus;
- God is perfect in every single possible way
- Existence is essential to perfection, if something does not exist then it has a limitation thus is not prefect. So, things that are perfect must exist
- Therefore, God exists.
By simply looking at the definition of words, we see that the conclusion must be the case. Descartes, didn’t stop there, he went on to prove the external world. He stated that only three things can cause what we see; God, demon or the external world. As he has already established, God exists so if a demon was deceiving us then God cannot be perfect if he is allowing us to be deceived and so can not be the demon as God is perfect. The cause for world can not be God as it is his nature to be perfect and thus he wouldn’t make it so we are easily deceived. Descartes then concludes that there must really be an external world. By considering the options, looking at the definitions, Descartes deduces that the external world must exist.
Using just a priori intuition and demonstrations, Descartes has show four things that exist in the world; his mind, God and the external world. He has also asserted his body can live without the mind, yet another fact that has been proved through a priori intuition.