Frank Jackson’s knowledge argument, which is based on a thought experiment about Mary, a brilliant neuroscientist, living in a black and white surrounding, is one of the most important challenges for physicalistic conceptions of the mind. The argument roughly aims at indicating that a complete physical knowledge of the world, would not include the knowledge of phenomenal properties of experience, therefore physicalism is false. In addition to his anti-physicalist thesis, Jackson further claims that phenomenal qualities of experiences are epiphenomenal. However, according to the inconsistency objection that is based upon a causal theory of knowledge, the knowledge argument undermines epiphenomenalism, because gaining the knowledge of phenomenal experience requires that phenomenal states are causally potent. However, the criticism can be challenged by developing a causal account of phenomenal knowledge without attributing a causal function of phenomenal properties. In this paper, it will be claimed that such a causal account is possible based on the notions of “reliability” and of “common causal origin” phenomenal experience and phenomenal knowledge, hence that epiphenomenalism and the knowledge argument are not necessarily inconsistent.