ABSTRACT
Cartesian skepticism questions our belief in the natural world. We hold numerous beliefs about the natural world; some of them are perceptual beliefs based on our sensory experience while others are testimonial beliefs based on reports from others. Those beliefs may be preserved in memory, and then combined and extended by deductive and inductive reasoning. Of these types of beliefs, the target of the Cartesian skeptic is perceptual beliefs because they are the most fundamental about the natural world. Testimonial beliefs are dependent on sensory experience in two ways. We receive testimony through our own sensory experience either by hearing it or by reading it. Further, if a report on the natural world is to be trusted, someone must have had sensory experience that supports its content. The report may be preserved in memory and passed on through a chain of communication, but someone at the origin of the chain must have had appropriate sensory experience at some point. Similarly, if my memory of the natural world is to be trusted, I must have had sensory experience in the past that supports its content. Inference may extend our beliefs about the natural world, but they are not the original source. So, if our perceptual beliefs cannot to be trusted, then our beliefs about the natural world are in serious doubt.
