 At the basis of Gibbs’ approach stands a conceptual shift. The object of study in the Boltzmannian framework is an individual system, consisting of a large but finite number of micro constituents. By contrast, within the Gibbs framework the object of study is a so-called ensemble: an imaginary collection of infinitely many copies of the same system (they are the same in that they have the same phase space, dynamics and measure), but who happen to be in different states. An ensemble of gases, for instance, consists of infinitely many copies of the same gas bit in different states: one is concentrated in the left corner of the box, one is evenly distributed, etc. It is important to emphasise that ensembles are fictions, or ‘mental copies of the one system under consideration’ (Schrödinger 1952, 3); or alternatively they can be thought of as collections of possible states of the entire system. Hence, it is important not to confuse ensembles with collections of micro-objects such as the molecules of a gas!