Why does Brown being in Barcelona have anything to do with Jones owning a Ford?

Surely examples such as "a stopped clock tells the time twice a day", and many other examples people have come up with since first reading Gettier, (such as sheep being in a field when you saw a white poodle) work much better than Smith thinking that Jones owns a Ford and Brown is in several places one of which is Barcelona, which happens to be true. Do people tend to quote the first case, the 10 coins one, because it is a better example, even though it's still not as good as the stopped clock? There doesn't seem to be much in the way of justification in the 2nd case - there are reasons for thinking Jones owns a Ford but no reasons for thinking Brown is in Barcelona so how can you deduce that from the first premise, that Jones owns a Ford? If Smith merely "constructs 3 propositions" about Brown's whereabouts, he clearly doesn't believe any of them, so this is not even a case of JTB anyway.

So the problem according to the first answer I have been sent is the rule of disjuction introduction is regarded as justification. But why should "I know that J entails [ J or] B"? - it's simply set it up as "either/or"? You're a Philosopher or my name is Santa? So, stating it again: S justifiably believes P which happens to be false and bases his belief in Q (why?) - (which happens to be true) on P. Since P logically implies Q (why?), S knows it does, S has excellent (really?) reason (P) for believing Q. Gettier famously claims S does not know that Q, despite JTB in Q. How is it justified to merely apply a logical connective "either/or". Am I really justified in believing either there is a wasp in my kitchen or I am out of milk? Just a random connective surely? (And not the best example of what he was trying to show.)

OK, so there was not a wasp in my kitchen and I had run out of milk. Or there was a wasp in my kitchen but I had not run out of milk. In either case if this was true, it was not knowledge that I thought about it beforehand and made a proposition about it. Did I really believe there was a connection between a wasp and whether I had milk? Did S really believe there was a connection between Jones owning a Ford and Brown being somewhere? So the example wasn't even JTB in the first place as there was no B.

  • If you're not a philosopher then my name is Santa!
    – Scott Rowe
    Nov 2, 2022 at 20:53

1 Answer 1


They have nothing to do with each other, and that's the point.

It seems a reasonable principle that if I have strong evidence or justification for some proposition A, and A logically entails B, and I know that A entails B, and I knowingly infer B from A, then I have strong evidence or justification for B. We might call this principle the closure of justification under known entailment. (There are actually potential exceptions to it, such as the paradox of the preface, but we needn't worry about that here.)

So, let B be "Brown is in Barcelona" and J "Jones owns a Ford". Now suppose I believe J and have strong justification for it. I know that J entails J or B - this is the rule of disjunction introduction. So I have strong justification for J or B. But if it should turn out that J is false and B is true, then my belief in J or B is true and justified, but hardly constitutes knowledge, because I was just lucky. So it is a Gettier case because it is an example of a justified true belief that fails to be knowledge.

  • 1
    So either Jones owns a Ford or your name is Father Christmas - I am so sure that Jones owns a Ford. Turns out you changed your name by deed poll to Father Christmas. Wow, I knew it! (Clearly I didn't though. Which is Gettier's point.) But I never believed your name was Father Christmas. Surely you must believe that p entails q? or it is not JTB anyway. Nov 8, 2015 at 12:01
  • In most circumstances it is strange to infer P or Q from P, because it seems to be losing information. But it is still a valid logical consequence, which is all that is needed to generate Gettier examples. Bear in mind also, that what appears to be a disjunction depends on what words are available in your language. If your language contains words for brother and sister, but not sibling, then you can only say sibling disjunctively. If your language contains sibling but not brother or sister, then you can only say brother through a conjunction of sibling and male.
    – Bumble
    Nov 8, 2015 at 16:03

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