 It’s also worth noting that although talk of acquaintance often brings sense-datum theory to mind, there is nothing about the commitment to acquaintance itself that entails such a commitment. According to sense datum theory, whenever one has a sensory experience as of some object having some property F, there is some object present that has the property F. For example, if I have a sensory experience as of a green triangle, then there is something present that is green and triangular. And since I could have this sensory experience even while hallucinating (at least according to sense datum theorists), this object that is green and triangular is not a physical object. In contrast to the sense datum theorist who treats the sensed property F as a feature of some object of which the subject is aware, the adverbialist or advocate of the theory of appearing treats it as a way of sensing or experiencing. To dance a waltz is not to do something or perform some act, viz., dancing, that takes something else, a waltz, as its object, but is rather a way or manner of dancing—dancing waltzily; similarly, to experience or have an appearance of green is not to have an act of awareness that takes a green object as its target, but is rather a way of experiencing or being appeared to—“experiencing greenly”, or “being appeared to greenly.” The acquaintance approach is compatible with adverbialism regarding sense experience; one might be acquainted with experiential states, and with one’s experiencing greenly, as opposed to being acquainted with some green object, and with its being green. (See, for example, Fumerton 1985: 94–5; McGrew 1995: 93–4; and Chalmers 2010: 291.) Alternatively, some acquaintance theorists take perceptual or sensory experience to involve acquaintance with universals, and hope thereby to avoid problems with both the sense datum theory and the adverbial theory. For an interesting defense of this view, see Forrest (2005). (For more on sense datum theory and adverbialism, see the entry on  the problem of perception.)