Philosophia: International Journal of Philosophy ISSN 2244-1875 Vol. 24, Number 1, January 2023  Volume 24, 1: 2023 FACTS, ABILITIES AND CONCEPTS: KNOWLEDGE ARGUMENT AND PHYSICALISM Jose Ramon E. de Leon Bicol University, Philippines Napoleon M. Mabaquiao, Jr. De La Salle University, Philippines One compelling argument challenging the tenability of physicalism, which sees reality as fundamentally comprised of physical facts, is Jackson's knowledge argument. Through a powerful thought experiment involving the case of Mary, the super neuroscientist, the argument demonstrates how knowledge of phenomenal facts cannot be deduced from knowledge of physical facts. For allegedly leaving out phenomenal facts in its account of reality, physicalism is shown to be incomplete and hence mistaken. Physicalists respond to this argument in a variety of ways, challenging, in turn, some aspects of the knowledge argument. This paper focuses on the replies of the ability hypothesis and the phenomenal concept strategy, which respectively try to block the two crucial moves in the knowledge argument: the establishment of an epistemic gap and the inference from the occurrence of this gap to the existence of an ontological gap. The paper critically examines how proponents of these two replies to the knowledge argument respond to some objections to maintain the viability of physicalism. Keywords: ability hypothesis, knowledge argument, physicalism, phenomenal concept strategy, qualia INTRODUCTION Physicalism, as a metaphysical view, contends that the fundamental facts that comprise reality are physical in kind. In relation to minds and mental states, which are intuitively regarded as non-physical, physicalism, in the area of philosophy of mind, has generally come to be known as "the view that the mind is a purely physical part of a purely physical world" (Jackson 2004, 21). With regard to the relation of phenomenal truths (i.e., truths about subjective conscious experiences) and physical truths (i.e., truths about objective physical phenomena), physicalism is "the thesis that the phenomenal, or experiential, truths supervene with metaphysical necessity on the physical truths" (Stoljar 2005, 472).