In recent decades, one of the most widely debated questions in the philosophy of mind has been whether consciousness is physical or nonphysical. Jackson's knowledge argument, which argues that there are truths about consciousness that cannot be deduced from physical truths and infers that physicalism is false, has attracted interest since its appearance in 1982. In this paper, I examine the three major physicalist replies to the argument.<br>I first clarify what the argument requires of physicalists: they must show that physicalism is as compatible as property dualism with the following two intuitions: (i) no amount of nonphenomenal knowledge suffices for phenomenal knowledge (empiricism about phenomenal knowledge), and (ii) the object of a piece of empirical knowledge is a fact. I next point out that there are two options a physicalist who accepts (i) and (ii) might take: (A) to refute the knowledge argument and nevertheless satisfy (i) and (ii); (B) to show that physicalism can accept the argument and satisfy (i) and (ii). In the final section, I examine the three major (A)-type responses to the argument: the Non-Propositional-Knowledge View; the Old-Fact/New-Mode View; and the Incomplete-Physical-Knowledge View.<br>The conclusion I draw is this: the first reply fails to establish the invalidity of the argument; the second fails to satisfy intuition (ii); the third succeeds in satisfying both intuitions, but only in a negative way. It therefore appears that (B) is the more preferable option for a physicalist to adopt.