CONCLUSIONS
I have noted two reasons that scientists do and should ignore typical philosophical theories of objective evidence. First, these theories furnish concepts that are much too weak to give scientists what they want from evidence, namely, a good reason to believe.
Second, they furnish concepts that make the evidential relation entirely a priori. But frequently scientists try to discover whether evidential claims are true not solely by a priori reasoning but by empirical investigation. This, I think, follows from the idea of providing a good reason to believe. Some fact can be a good reason to believe a hypothesis even if this cannot be demonstrated by a priori calculation. If one seeks to define an a priori concept of evidence based, e.g., on the Carnapian idea of justification, the concept of evidence produced will require too many specific facts about an investigator to be of much interest to scientists generally.However, not wishing to end on too negative a note, let me close with a challenge to philosophers of science. It is to propose and defend a concept of evidence that is at once empirical and robust. It is empirical because, in general, it renders the question of whether e is evidence that h an empirical question, which scientists can attempt to answer using that concept. It is robust in two ways. It is a strong, not a weak, concept of evidence, and it is one that yields a good general reason to believe something, rather than one that must be tied to specific epistemic situations. If it is empirical and robust in these ways then, I think, it should be of interest to scientists.