Descartes devised his system of methodic doubt in order to discover an indubitable belief, which he could use as a certain, and secure foundation as the basis for knowledge. For Descartes it was necessary to look inside himself at all the beliefs he once held as true, and subject them to the strongest of doubts. For the purpose of freeing himself from all preconceived opinions, he allowed himself to believe that all his past beliefs were false and imaginary, as he states in the first meditation: " So, for the purpose of rejecting all my opinions, it will be enough if I find in each of them at least some reason for doubt." (Cottingham 1984, p12). This provided Descartes with t

he easiest path by which to lead the mind away from the senses. In considering how far doubt can be extended, he begins by questioning his sense perception.

Descartes realises that everything that he has up till now accepted as true has been acquired either from the senses or through the senses. However there have been times when he has found that his senses can deceive, such as when objects may appear differently from various points of view, and that therefore it is highly probable that other things which appear certain through the senses may in reality be illusions. On further reflection, Descartes ponders the proposition of being asleep or awake. He wonders if this is something that cannot be doubted. However he soon realises that there have been times when he has been asleep and dreaming of the same experiences he had when awake. Descartes argues: "How often asleep at night, am I convinced of just such familiar events-that I am here in my dressing-gown, sitting by the fire-when in fact I am lying undressed in bed!" (Cottingham 1984, p13). Descartes comes to realise that dreaming and reality are so blurred that he cannot know if anything occurring is true or false and that therefore the external world may be an illusion. Descartes thus asserts that all the knowledge derived from the senses cannot be regarded as absolutely certain.

Finally, Descartes considers whether material things exist. For Descartes, God guarantees that all the stuff in his mind must come from the stuff outside his mind and because God is not deceitful, God is the guarantee that there is something corresponding to all that stuff, as Descartes affirms:

"Now, however, I have perceived that God exists, and at the same time I have understood that everything else depends on him, and he is no deceiver; and I have drawn the conclusion that everything which I clearly and distinctly perceive is of necessity true. (Cottingham 1984, p48).

Descartes proceeds in his demonstration of the existence of God by analysing the nature of thought, for Descartes there are three kinds of ideas: ideas, which he invents, ideas, which appear to be, and ideas, which are innate. For Descartes the most important ideas are innate which he finds in his mind, he knows that he is

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