Foundations: A Defense of Ethical Contextualism (1999), Mark Timmons provides a reconstruction of Mackie's views in the form of the two related arguments. These are based on the rejection of properties, facts, and relationships that do not fit within the worldview of philosophical naturalism, the idea "that everything—including any particular events, facts, properties, and so on—is part of the natural physical world that science investigates" (1999, p. 12). Timmons adds, "The undeniable attraction of this outlook in contemporary philosophy no doubt stems from the rise of modern science and the belief that science is our best avenue for discovering the nature of reality". There are several ways in which moral properties are supposedly queer: our ordinary moral discourse purports to refer to intrinsically prescriptive properties and facts "that would somehow motivate us or provide us with reasons for action independent of our desires and aversions"—but such properties and facts do not comport with philosophical naturalism. given that objective moral properties supposedly supervene upon natural properties (such as biological or psychological properties), the relation between the moral properties and the natural properties is metaphysically mysterious and does not comport with philosophical naturalism. a moral realist who countenances the existence of metaphysically queer properties, facts, and relations must also posit some special faculty by which we have knowledge of them. Responses and criticisms Christine Korsgaard responds to Mackie by saying: Other criticisms of the argument include noting that the very fact that such entities would have to be something fundamentally different from what we normally experience, therefore assumably outside our sphere of experience, we cannot prima facie have reason to either doubt or affirm their existence. Therefore if one had independent grounds for supposing such things to exist (such as a reductio ad absurdum of the contrary) the argument from queerness cannot give one any particular reason to think otherwise. An argument along these lines has been provided by e.g. Akeel Bilgrami. Argument from explanatory impotence Gilbert Harman argued that we do not need to posit the existence of objective values in order to explain our 'moral observations'. See also Citations Bibliography . Further reading Garner, Richard T.; Bernard Rosen (1967). Moral Philosophy: A Systematic Introduction to Normative Ethics and Meta-ethics, New York: Macmillan. Garner, Richard T.; (1994). Beyond Morality. Temple University Press. Shafer-Landau, Russ (2003). Whatever Happened to Good and Evil?, Oxford University Press. Shafer-Landau, Russ & Terence Cuneo (eds.) (2007).