Etiological information and diminishing justification

Sometimes it’s reasonable to reduce confidence in a proposition in response to gaining etiological information. Suppose, for example, a theist learns that her theism is ‘due to’ her religious upbringing. There is a clear range of cases where it would be reasonable for her to respond by slightly decreasing her confidence in God’s existence. So long as reasonability and justification are distinct, this reasonability claim would appear consistent with the thesis that this kind of etiological information cannot, all by itself, affect one’s justification. In what follows, I argue that this is mistaken. For, even if reasonability and justification are distinct, the reasonability of decreasing confidence in response to etiological information must be explained in terms of a decrease in justification. The argument to follow threatens not only the stronger thesis that etiological information never defeats justification but the substantially weaker thesis, advocated by various authors, that justification is defeated by etiological information in only a limited range of circumstances. I go on to show how the arguments en route to this conclusion have much wider epistemological ramifications.