I here argue against the viability of Peter Ludlow’s modified version of Paul Boghossian’s argument for the incompatibility of semantic externalism and authoritative self-knowledge. Ludlow contends that slow switching is not merely actual but is, moreover, prevalent; it can occur whenever we shift between localized linguistic communities. It is therefore quite possible, he maintains, that we undergo unwitting shifts in our mental content on a regular basis. However, there is good reason to accept as plausible that despite their prevalence we (...) are in fact able to readily adapt to such switches, as well as to the shifts in mental content that accompany them. The prevalence of slow switching between linguistic communities does not then necessarily entail incompatibility after all. (shrink)