Jonathan Schaffer’s The Debasing Demon [.pdf] was an immense pleasure to read. Some highlights:
I will draw three lessons from the debasing demon. The first lesson is that all knowledge is imperilled by sceptical doubt, even knowledge of the cogito. This clarifies the range of scepticism. The second and related lesson is that anti-sceptical strategies relying on a residue of knowledge immune from doubt cannot succeed. The debasing demon leaves no residuum. The third lesson is that deception and debasement do not exhaust the forms of sceptical doubt. In that sense, there are more demons in epistemic hell than are dreamt of in epistemology. (Schaffer, 228)
… truth is not the only requirement for knowledge, and so not the only haunt for demons. On the orthodox post-Gettier view, knowledge requires not just truth but also evidence, belief, and the proper connections between these conditions. These connections include (i) a connection between truth and evidence, proper when the evidence is non-accidentally connected with the truth; and (ii) a connection between evidence and belief, proper when
one’s belief is based on the evidence.
The debasing demon preys not on the truth requirement but rather on the basing requirement. She throws her victims into the belief state on an improper basis, while leaving them with the impression as if they had proceeded properly. So for instance, the debasing demon might force me into believing that I have hands on the basis of a blind guess or mere wishful thinking, while leaving me with the impression as if I had come to this belief on the basis of the visual evidence. (231)
I could presumably come to my belief that I have hands on the basis of the visual evidence, or I could come to it on the basis of wishful thinking. Here are two routes, only the first of which is epistemically proper. But I could have come to the belief that I have hands on the basis of wishful thinking, while having the false impression that I came to this belief on the basis of the visual evidence.To think otherwise would be to suppose that I have infallible access to some of the mental transitions in my past. (232, bolding mine)
Deception and debasing are not the only haunts of demons, for truth and proper basing are not the only requirements for knowledge. On the orthodox post-Gettier view, knowledge requires not just truth but also evidence, belief, and the proper connections between these conditions. On this view, knowledge may be thought of as arising from a process starting from some worldly truth and culminating in apt belief:
Truth –[Non-accidentality]–> Evidence –[Basing]–> Belief
This picture of the process by which knowledge arises allows one to distinguish various sceptical threats. What a demon does may be characterized as follows. First, a demon dooms some non-final stage of the process (before belief), so that knowledge cannot arise. Second, the demon disguises some later stage (after the doomed stage) so as to erase the traces of doom.
And so, on the orthodox picture, there are actually ten different sorts of demon to be dealt with. A demon could doom the truth condition but disguise any of the four later stages of the process, or doom the non-accidentality condition but disguise any of the three later stages of the process, or doom the evidence condition but disguise any of the two later stages of the process, or doom the basing condition but disguise the remaining belief condition. (235)