“Imagination” is said in at least three major ways. Aristotle minimalistically characterized phantasia as a production of images that both plays a role in our experience of sense perception and can operate independent of it, as in dreaming. Spinoza treated imagination as kind of a passive belief. For him, this was strongly associated with common illusions and wishful thinking – especially with regard to our status as agents — in ordinary life. The Romantics identified imagination with creativity.
Beatrice Longuenesse in her marvelous Kant and the Capacity to Judge has developed in detail Kant’s argument that the same basic “categories” used in reflective thought are already implicit in our pre-reflective apprehensions of things in what Kant called a synthesis of imagination. I think this means not that the Kantian categories have some pre-given or metaphysical status, but rather that for the kind of beings we are, even “pre-reflective” apprehensions have some dependency on previous reflective apprehensions. We are never either entirely active or entirely passive. (See also Passive Synthesis, Active Sense; Voluntary Action; Middle Part of the Soul.)
Richard Kearney in On Paul Ricoeur: The Owl of Minerva nicely develops Ricoeur’s view that imagination is not so much a special way of seeing as “the capacity for letting new worlds shape our understanding of ourselves…. This power would not be conveyed by images, but by the emergent meanings in our language” (quoted in Kearney, p. 35). According to Kearney, Ricoeur associated imagination first and foremost with “semantic innovation”. What Aristotle in a different context called “searching for a middle term” is an aspect of this creativity with respect to meaning.
The Greek root for “poetry” (poiesis) fundamentally means making or doing in a much more general sense. The Romantics added a stress on innovation, which they saw as coming from the inner depths of the soul. Ricoeur’s treatment of imagination as fundamentally involving the emergence of new meaning nicely takes up the Romantic stress on imagination as innovation, without depending on the Romantics’ dubious metaphysical psychology of interiority. (See also Personhood; Reason, Nature.)