  Ayer’s particular analysis, or one closely resembling it, came under attack in a famous paper by Gettier (1963), in which satisfaction of the three clauses (the truth of p, the belief in p, and the right to be sure that p) was held to be insufficient for knowledge.  Gettier’s argument requires that someone, A, could be justified in believing a false proposition, and that if A was justified in believing p and q is deducible from p, and A accepted q by deducing it from p, then A would be justified in believing q. An example used by Gettier has the following structure: (i) Jones owns a Ford. (ii) Either Jones owns a Ford or Brown is in Boston. Smith believes, and has ample evidence for, (i). He deduces (ii) from (i), and so is justified in believing (ii), even though, in fact, he has no idea of where Brown is. It turns out that (i) is false, but (ii) is true – unbeknownst to Smith, Brown is indeed in Boston. Gettier concluded that in this case all three clauses of the analysis of knowledge are satisfied, but that we should judge in this case that Smith did not know (ii). The suggestion was that additional clauses might be needed.