Eighteenth-century constructions of sensibility draw on imagination as a pivotal term, but theories about the activity of imagination are as widely varied as theories of sensibility. Some hold the imagination to be governed by the senses themselves; others define imagination as the faculty that processes sensory data to produce a feeling response; still others see imagination not as coeval with sensibility, but as able to manipulate feeling in order to produce the creative work of art or the political work of compassion. While Addison says that imagination is a product of human cultivation, which will only be strengthened with the further development of the race, Blair calls imagination primitive, that which has been banished and which has, in its wake, left the flaccid effusions of minds which understand neither tenderness nor sublimity. Diderot and Lord Kames see the imagination as a sort of training ground for real worldly interaction.
In any given discourse of sensibility, imagination tends to take on a stable, well-defined role, yet it always holds open the possibility of spinning out of control. One concern is that although the imagination can be liberating, it can also be binding. When Gray, in "The Progress of Poesy," calls on the Muse to free him from scenes of despair, his musings become more and more desperate. Yorick, as he imagines a Bastille prisoner, oppresses the prisoner as well as himself as he heaps misery into the imagined scene. Imagination can also lead to self-indulgence in its attempts to magnify its own power; Mackenzie consequently worries that the sentimental reader is more concerned with acting on the pure imagination than the sound one.