An inquiry into the human mind, on the principles of common sense By Thomas Reid
I have on occasion seen this represented as a 'madness' argument against skepticism, i.e., the argument that it would be simply mad to be a skeptic. But this is not, I think, accurate. The passage is not primarily an argument against skepticism at all; it is a diagnosis of it, namely, as a form of madness, and, without explicitly stating a cure, obviously suggests one -- namely, interaction with society. But a diagnosis of a particular instance of a philosophical error is only an argument against it for those who share the account underlying the diagnosis; and a general diagnosis of a kind of philosophical error is not really an argument against it at all, but a classification of it assuming that it is, indeed, an error or, at least, a malady (since the two need not coincide perfectly).
However, it is closely related to a common argument against skepticism, namely, the apraxia objection, the argument that skepticism would make practical life impossible. This bothered Hume enough to consider the matter; and we find the answer in Treatise 1.4, especially (but not exclusively) in 1.4.7. Reid's diagnosis is interesting in that it is a diagnosis of skepticism derived from Hume, the person who, for Reid, is almost a paradigm example of a skeptic. In making this diagnosis, Reid is simply building on Hume's own diagnosis of the situation, since Hume makes the same diagnosis, calling it a "philosophical melancholy and delirium" and also regards it as intermittent, dissipating on exposure to society. Thus it is important to note that you can be a skeptic and agree with Reid's diagnosis; Hume is the prime example, since, in fact, Reid's diagnosis is simply taken from Hume.
