Descartes" first meditation is the preliminary answer in reply to the skeptic view point. Descartes uses doubt in order to respond to skepticism and in turn uses the thinking against itself. He begins by examining the three principle ways of how knowledge is gained; senses, reality and mathematics. In all three examinations Descartes builds a foundation for each argument and then discredits them through the method of doubt. .
Descartes begins with examining the senses, for they are the principle means of knowledge reception. Everything is gathered through these five senses. Everyone possesses these senses and experience is obtained through them. However, Descartes proves that our senses may easily be deceived and if deceived once they cannot be trusted. He uses the example of distance and the true size of an object to doubt our perception. Even if our senses may not always be trusted Descartes allows for the senses to be used under optimal conditions and to aid in the explanation of the second subject; reality.
One understands that our senses, under optimal conditions, will not always deceive the being. Descartes constructs reality as our waking state for it is another means of how knowledge is conceived. This candidate is then discredited by the dream argument. Descartes tests reality through the waking and dreaming states that one experiences. These states of mind can be discredited by the work of our imagination. Descartes points out that there is no definite or defining characteristics to distinguish between reality and imaginary dream states. .
Lastly, Descartes considers the concept of mathematics. Mathematics has a specific foundation relying on the fact that there is always a concrete and definite answer despite the differing reality and dream states. Descartes then questions if thoughts may be deception. What may be true in his mind may be different from the truth that the all powerful God had created or intended for.