In this post, I will discuss the ways in which dreams pose risks to the certainty of experience and how local and global skeptics differ in this analysis.

With respect to dreams, a local skeptic might suspend confident belief in a specific sensation, experience, or memory, pointing to the distinct possibility of said phenomenon occurring within a dream. Such local skeptics would maintain the plausibility of misperceiving any experience due to such a possibility. They would call upon neuroscientific advances and logical reasoning in order to try and determine the likelihood of an experience occurring within a dream. For instance, in Descartes' Sixth Meditation, he introduces his coherence test, an algorithm for confidently discerning what is real. He says:

"But when I perceive objects with regard to which I can distinctly determine both the place whence they come, and that in which they are, and the time at which they appear to me, and when, without interruption, I can connect the perception I have of them with the whole of the other parts of my life, I am perfectly sure that what I thus perceive occurs while I am awake and not during sleep." (Meditation VI. 24)

Descartes' specific test here is not particularly important, but serves as an example of how local skeptics have sought to ground their determinations of such perceptions in science. There exists countless semi-scientific "techniques" a person can supposedly call on to determine whether they are dreaming. Most of these tricks depend on some notion of "normality". For instance: squishy walls, incoherent newspapers, faulty light switches. All of these techniques seek to contrast some "dream dynamic" with what is expected based on some learned notions of normality.

The crucial dynamic here is actually more binary than probabilistic. I argue it is not particularly important the frequency with which one might find themselves in the "grey area" of this technique - wherein they cannot whole-heartedly carry a perception through this algorithmic scrutiny. Rather, the interesting bit is the supposition that there are, however infrequent, perceptions that one can be "perfectly sure" occurred while they were awake. And herein lies the disagreement. A local skeptic need not subscribe to any specific litmus test, all that matters is whether one believes it is inherently possible to positively determine an experience to be actual, and not having occurred in a dream or other experiential medium.

A global skeptic, on the other hand, would find any notion of a coherence test utterly implausible. How can we say for certain that the perceptions and experiences which have led to the formulation of such a test have not themselves fallen victim to the very sorts of misleading misperceptions we mean to investigate in the first place? If one finds their test even tenuously dependent on expectations learned from previous experience, then they have found themselves within a vicious feedback loop. Why should self-proclaimed 'local skeptics' feel comfortable leaning on perceptions and other experiences with which they have no more reason to rule out as fictitious dreams than those which they mean to investigate? They would have irreversibly forfeited any notion of "true experience"; could it not be supposed that one's entire life up until this point has merely been a dream itself? If we maintain that there exists some perceptions which are fabricated entirely within a dream, then we must surrender to the idea that perhaps truly none of our beliefs and perceptions are true and justified in a conventional sense.