Abstract: It seems that if a thinker in an argument arrives at an empirical conclusion, then some of the belief-formation or reasoning principles she employs must be a priori if the reasoning is to be knowledgeable. Michael Friedman investigates the existence of empirically defeasible a priori warrants, focussing on the principles that are constitutive of the spatio-temporal framework within which a particular scientific theory is formulated.

Keywords: a priori, a priori knowledge, Michael Friedman, Kantian, reasoning, scientific theory, spatio-temporal framework, warrant,