For external world propositions to serve as evidence against skeptical hypotheses, Closure and Transmission principles would need to coincide — i.e., evidence for p would need to be evidence for every q entailed by p
Transmission principle(Dretske is accused of conflating Closure with Transmission in the mule case)
An epistemic principle stating that evidence for p is also evidence for any q entailed by p — a stronger condition than mere Closure
external world propositions(as used in epistemology)
Statements about things that exist outside your mind, like 'There is a table in front of me' or 'The sun exists.'
skeptical hypotheses(Cartesian epistemology and global skepticism)
Hypotheses that are empirically equivalent to our ordinary picture of reality but posit radically different underlying circumstances, such as an evil demon deceiving us or our being brains in a vat connected to a supercomputer
The Cartesian skeptic can nevertheless raise an uncomfortable question at this point: what is this alleged evidence in favor of the proposition that we are not in a skeptical scenario? One tempting answer is that the evidence in question consists precisely of those external world propositions which are the target of the Cartesian argument. I know that I have hands, and, according to this view, that very proposition is my evidence for the proposition that I am not a handless brain in a vat. But r