Robert Nozick states that in order to know we need to satisfy the following four conditions:

S knows that p iff

  1. p is true,
  2. S believes that p,
  3. If it weren’t that case that p, then S wouldn’t believe that p,
  4. If it were the case that p then S would believe that p.

This is a basic version of Nozick’s account of knowledge, where the conditions (3) and (4) are truth trackers.

Let’s try to apply this account of knowledge to Gettier case, Dretske’s Lava, Barn case, Brain in a vat case, Dictator case and Faith case.

Gettier Case: condition (3) is not satisfied. If it weren’t the case that Jones does not own a Ford, Smith would still believe that Jones owns a Ford.

Dretske’s Lava: If it’s not the case that p, I still have the reason (identical evidence Lava solidified) and I would still believe that M erupted, thus condition (3) is not satisfied.

Barn Case: While driving though the countryside, Henry identifies an object as a barn. Let us suppose that unknown to Henry, the region is full of expertly made papier-mâché facsimiles of barns. In a new possible world, if it weren’t the case that p, we would still believe in p. Thus, condition (3) is not satisfied.

Brain in a Vat Case: Imagine that my brain is in a vat and I am brought to believe that by direct electrical and chemical stimulation of my brain. Thus, condition (3) is satisfied. If my brain was not in a vat, I wouldn’t believe it is. But imagine the world where my brain is in a vat, but it is not electrically stimulated giving me belief. In this case, i would not belief that my brain is in a vat. Even if it is true that my brain is in a vat, I would continue to not believe that my brain is in a vat. Consequently, condition (4) of Nozick’s account is not satisfied.

Dictator’s case: The dictator of a country is killed (p). In their first edition, newspapers print the story, but later all the country’s newspapers and media deny the story, falsely. Everyone who encounters the denial believes it or does not know what to believe and suspends judgment. Only one person in the country fails to hear any denial and he continues to believe the truth. He satisfied conditions (1)-(3), yet (4) is not satisfied. If he heard the denials he too would have believed them, just like everyone else. His belief is not sensitive to the truth. Thus condition (if p were true, S would believe that p) is not satisfied.

Faith case: A father believes that his son is innocent of committing a particular crime, both because of faith in his son and because he has been presented in the courtroom a conclusive demonstration of his son’s innocence. His belief via the method of courtroom demonstration satisfies conditions (1)-(4), but his faith-based belief does not. If his son were guilty, he would still believe him innocent on the basis of faith. Thus, his belief that P via faith in his son violates condition (3). It’s too demanding to ask that every method should satisfy (1)-(4). Though, it’s not good enough that there is at least one method that satisfies (1)-(4). The method of faith outweighs the method of evidence if faith is unconditional in this case. Even if courtroom demonstration would lead to the belief that his son is guilty, that not-p, still father would believe his son innocent via faith in his son.

Nozick’s solution here is to add a rule of multiple methods:

S knows that p if there is some method via which S believes that p which satisfies conditions (1)-(4), and that method is not outweighed by any other method(s) via which S actually believes that p, that fail to satisfy conditions (1)(-4).

So, the final version of Nozick’s account of knowledge is as follows:

S knows via method ( or way of believing) M that p iff:

  1. p is true,
  2. S believes, via method or way of coming to believe M that p,
  3. If p weren’t true and S were to use M to arrive at a belief whether (or not) p, then S wouldn’t believe, via M, that p.
  4. If p were true and S were to use M to arrive at a belief whether (or not) p, then S would believe, via M, that p.

S knows that p iff there is a method M such that:

  • He knows that p via M (evidence), his belief via M that p satisfies conditions (1)-(4),
  • All other methods M1 via which he believes that P that do not satisfy conditions (1)-(4) are outweighed by M.

Bibliography:

  • Kripke, Saul A., 2011, “Nozick on Knowledge”, in Philosophical Troubles: Collected Papers, Volume 1, Oxford: Oxford University Press, pp. 162–224.