 The All-in-One principle is not beyond doubt. One application of plural quantification, which is explored by Cartwright (1994), is to abandon the All-in-One principle and to understand talk of a domain of quantification not as singular talk of collections but rather as plural talk of its members. To speak of a domain of certain objects is just to speak of the objects themselves—or to speak of a first-level concept under which they all fall; and to claim of a given object that it lies in the domain is to claim of the object that it is one of them. Alternatively, one may opt for the expressive resources of second-order quantification with the second-order quantifiers taken to range over Fregean concepts. Williamson (2003) outlines a conception of a domain of quantification as a Fregean concept under which certain objects may fall. To speak of a domain of all objects on this view is to speak of a Fregean concept under which all objects—without restriction—fall, and to claim of a given object that it lies in the domain is merely to claim that the object falls under the relevant Fregean concept.