 The knowledge argument is often cited as one of those anti-physicalist qualia-based arguments that are supposed to justify property dualism. The above formulation, however, does not explicitly mention non-physical properties but only non-physical facts. But the relation between the two claims is obvious. Friends of the knowledge argument will say that the facts at issue are non-physical because they involve the exemplification of non-physical properties (e.g. of the property of having an experience with quality Q).