Hartry Field has recently presented an original and interesting approach to the a priori. Its main theses are, first, that certain rules are empirically indefeasible and, second, that the reasonableness of these rules are not based on any factual property. After an introduction, Field’s approach is presented in section II. Section III examines his claims concerning empirical indefeasibility. It will be argued that his general argument for empirical indefeasibility fails along with the particular examples of rules he gives. Alternative ways of preserving empirical indefeasibility are suggested that are compatible with overdetermination under certain assumptions. In section IV, Field’s arguments for the nonfactuality of epistemological concepts, such as reasonableness, are found wanting. At the end, an alternative way of understanding the link between the epistemological concept in question and truth-conduciveness is proposed that preserves the factuality of the epistemological concept.