Justification and Defeasibility, Theoretical and Practical

Is any justification absolutely indefeasible? This cannot be determined without a good understanding of what defeasibility is. There are two central cases: overriding and undermining. If undermining is complete, there was no real justification to begin with, whereas overridden justification can be simply weaker than the overriding element(s). This paper explores both kinds of defeasibility and appraises the case that certain kinds of justification are overridable but not underminable. This is a quite general thesis, and the paper argues that if we take seriously the analogy between justification in the realm of belief—the traditional focus of epistemology—and justification in the practical realm—the traditional focus of moral philosophy—we can see a stronger case for the existence of certain indefeasible sources of justification.