 A friend of the knowledge argument might concede that a person is acquainted with Q only if she has or had an experience with property Q but he would have to insist that being acquainted with Q in that sense is a necessary condition for being able to know (in the relevant sense) that an experience has Q. Another kind of criticism of the Acquaintance Hypothesis is developed in Gertler (1999). She argues that the property dualist can explain why the most direct way to get familiar with a quale is by having an experience of the relevant kind while the physicalist does not have any explanation for this particular feature of qualia. Similarly, Robert Howell (2007, 146) argues that all other physicalist responses to the Knowledge Argument depend upon the Acquaintance Hypothesis, and that acquaintance is incompatible with objectivism (see Section 4.9 below).