Towards an Objective Theory of Rationality

4. An Objectivist Epistemology

4.2 Criteria for Minimal Acceptance of Evidence

Book cover: The Logic of Scientific Discovery by Karl Popper

What are such fundamental criteria for rational theory appraisal? Every epistemology stipulates that the evidence qua evidence must be epistemically related to the theory under evaluation. The epistemic status of the evidence-statement must have some consequence for the epistemic status of the theory. In an objectivist theory of rationality, the evidence must partially determine whether the sentence or theory has the property of stating what is actually the case. Statements about the subjective states of people do not satisfy this requirement and so are not regarded as evidence. Debarred statements include statements that a person or a group of people:

  • believe/disbelieve the sentence or theory,
  • approve/disapprove of the political/ethical implications of the theory being believed by the general populace,
  • prefer the theory to be true/false,
  • consider acceptance of the theory more pragmatic,
  • consider the theory more aesthetic or more simple.

The above condition is the minimal requirement of independence; that a statement be independent of subjective states for it to be regarded as evidence. It should be clear that this requirement follows from the general requirements of an objectivist epistemology outlined at the start of this section.

That a statement be minimally independent is a necessary but not a sufficient condition for it to be regarded as evidence. As I said above, the statement must necessarily be epistemically related to the sentence or theory. This is satisfied by a requirement of logical entailment. Take the case of an explanatory theory T and auxiliary hypotheses A. (I include here auxiliary hypotheses A because explanatory theories do not normally entail evidence-statements in isolation. In this case, the evidence-statement e cannot be logically entailed by the auxiliary hypotheses alone.) If a theory T and acceptable auxiliary hypotheses A logically entail evidence-statement e, and e is false, then e is evidence against T.[8] If e is true, then e is evidence for T.

We may now state the necessary and sufficient conditions for a statement to be evidence for a theory. A statement is evidence for a theory iff:

Criterion 1:
the statement is true;
(requirement of dependence on epistemic value)
Criterion 2:
the statement is logically entailed by the theory in conjunction with accepted auxiliary hypotheses, but not by the auxiliary hypotheses alone;
(requirement of dependence on logical deducibility)
Criterion 3:
the statement is not a statement of the relationship between the theory and a subjective state or states.
(requirement of independence from psychological states)


  1. [8] 'N' =df 'it is logically true that'. N(N((T&A) → e)&(−e&A)) → −T) in the limit where A and −e are certain.

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