 There are two related tasks involved. First, philosophers have used other mental entities to define imagination by contradistinction (but see Wiltsher forthcoming for a critique of this approach). To give an oversimplified example, many philosophers hold that imagining is like believing except that it does not directly motivate actions. Second, philosophers have used other mental entities to understand the inputs and outputs of imagination. To give an oversimplified example, many philosophers hold that imagination does not output to action-generating systems.