In Meditations 1 the meditator looks at the foundations of his beliefs. For, if the foundation of one’s beliefs can be doubted then all those beliefs build upon that foundation cannot be true. Aristotelian physics is founded on sensory perception, if Descartes meditator can show that the senses may be doubted then he can seduce people to changing their beliefs. The meditator reasons that all beliefs that he has found most true have come from sensory experience such as sight, touch, smell, etc. In doing so he realized that his senses have deceived him before when it comes to things not so clearly perceived. For example when in the desert people often perceive water off in the distance, when in fact it is a mirage caused by the heat waves. Yet, as he dives deeper Descartes’ meditator asks if even the things he perceives so clearly such as the warmth of a fire next to him can be doubted. Then he asks himself how many times he has dreamed such dreams of himself being clothed next to the warm fire of his home when he is indeed undressed, sleeping in his bed. The meditator thus realizes that he has dreamed vivid and distinct dreams or at least that such dreams are possible. After coming to this realization he sees “that there are no definitive signs by which to distinguish being awake from asleep.” Therefore it is possible to be asleep with all of our perceptions at this time being false.
1. It is true that sometimes we mistakenly take objects to exist in reality when they really exist only in our dreams.
2. If this premise is true, then there is essentially no difference between illusory dream experiences and veridical waking experiences.
3. If there is no essential difference between illusory dream experiences and veridical waking experiences, then it is plausible for us to be dreaming all the time.
4. If we are potentially dreaming all the time, then none of our beliefs based on sensory experience are indubitable.
5. Therefore, we can conclude that no belief based on sensory experience is indubitable.