Rene Descartes 'Meditations'

In the Meditations, Rene Descartes attempts to develop stable foundations for knowledge. Descartes wants to break down the unstable and uncertain foundations that all his current knowledge is based on, in order to discover truth or certainty. Descartes argues that everything can be doubted, including all knowledge from the senses, and even simple mathematical principles, yet he searches for certainty in knowledge. However, Descartes does not provide a clear map for recognizing and achieving certainty, or even give sufficient reasons to believe the possible existence of absolute certainty in knowledge. Descartes argues that all knowledge from the senses can be questioned or doubted, since his senses have often deceived him.

For instance, Descartes argues that he has had dreams in which he believed he was definitely sitting by the fire, wearing a dressing gown like he usually does. However, he was actually lying on his bed naked. Descartes' sensory experiences of material objects and his own body in his dreams are as vivid and clear as his "real" experiences. This allows him to be tricked into believing his dreams are real. For this reason, he cannot tell the difference between being awake and dreaming with certainty. The sense perceptions during both states are extremely similar. He could be dreaming right now, even though he thinks he's really awake. If he is actually dreaming right now, then all his sense perceptions at the moment are false. However, it might not be the case that he's always hallucinating or dreaming what he perceives, but he is still sometimes tricked into

One instance of this is the Ebbinghaus illusion. In this illusion, we are shown a circle in the middle surrounded by much bigger circles. There is another circle in the middle next to the first circle surrounded by many smaller circles. We are asked "which of the two central circles is larger?" We reply the second one, since it appears to our eyes as the larger of the two circles. However, both circles are the same size, even though we are convinced they are different sizes. We see the size of the circles as relative to the other circles it is surrounded by. When the central circle is surrounded by bigger circles, then we perceive it as smaller. But when that same central circle is surrounded by smaller circles, then we perceive it as bigger. This shows that through our senses we are perceiving misleading information about the size of these circles, and probably other objects as well. We cannot know for certain if what we know through our senses is accurate in the presence of any such illusions. But kmowledge from our senses is usually or mostly accurate. This is still a big problem for Descartes though. He argues that it is reasonable to not believe or reject any beliefs that are not absolutely "certain and indubitable" (Meditation 1). Therefore, he thinks it is wise to regard everything he knows from his senses as doubtful and