Nozick’s Truth-Tracking Theory

The core idea of Robert Nozick’s truth tracking theory is that if one has a tendency to believe something when it’s true, and not believe it when it’s false, then one knows it. (Nagel, p. 62).

Here are three examples to illustrate:

  1. A chicken sexer knows the sex of a chick if she believes it is (not) a female chick when it is (not) a female check.
  2. A bank teller knows that he is dealing with fake money if he believes that a bank note is (not) fake when it is (not) fake.
  3. Neo, the protagonist of the Matrix movie, knows that he is lying in a vat if he believes he is lying in a vat when he actually does and if he believes that he is not lying in a vat when he actually does not.

A formal definition of Nozick’s truth-tracking theory:

S knows that p iff

  1. p is true
  2. S believes that p
  3. if p were not true, S would not believe that p (“sensitivity condition”)
  4. if p were true, S would believe that p (“adherence condition”)

Conditions 1 and 2 state what is actually happening in the world. Conditions 3 and 4 are subjunctive conditionals that state what would happen in circumstances different from the actual ones. These counterfactuals are the conditions that track the truth. (Nagel, p. 63) S’s diagnoses have to be sensitive to the situation in order for S to know that p.

Essentially, Nozick developed an “externalist” theory of knowledge. The factors that warrant S’s belief, and make it genuine knowledge, may be factors of which S is entirely unaware and which are external to S’s conscious cognitive processes (Feser). Nagel (2014, p. 63) notes that S can even be mistaken about the factors that determine her beliefs. The chicken sexer might work under the assumption that her chicken sexing capabilities are based on visual clues even though, unbeknown to the her, her selection capabilities might actually be determined by smell. On this account, the status of knowledge is independent from the method or mechanism which S’ deploys to form her beliefs so long as the method or mechanism accurately tracks the facts.

However, it is conceivable that someone tricks S into believing p even though p is not true. This would constitute a breach of condition 3 to the extent that S cannot be said to know anything about p anymore. One option for S would be to change over to another method of belief formation, one that hasn’t been compromised yet. It is this leaning on a method of belief formation that Nozick added to his truth-tracking theory later on (Nagel, p. 64).


Feser, Edward, “Robert Nozick (1938 – 2002)”, Internet Encyclopedia of Philosophy, Fieser, James, Dowden, Bradley (eds.), URL = <http://www.iep.utm.edu/nozick/>

Nagel, Jennifer, Knowledge – A Very Short Introduction, Oxford University Press, 2014

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