In "What is it Like to Be a Bat?", Nagel argues that consciousness has essential to it a "subjective character," a "what it is like" aspect. He states that "an organism has conscious mental states if and only if there is something that it is like to "be" that organism—something it is like "for" the organism." His critics have objected strongly to what they see as a misguided attempt to argue from a fact about how one represents the world (trivially, one can only do so from his own point of view) to a false claim about the world, that it somehow has first personal perspectives built into it. On that understanding, Nagel is a conventional dualist about the physical and the mental. This is, however, a misunderstanding: Nagel's point is that there is a constraint on what it is to possess the concept of a mental state, namely, that one be directly acquainted with it. Concepts of mental states are only made available to a thinker who can be acquainted with his/her own states; clearly, the possession and use of physical concepts has no corresponding constraint.