One of the key arguments that Coleridge outlines in this important work of criticism is his own interpretation of the word "imagination" and its importance in the creative process. For Coleridge, he saw imagination as being so important and essential that he split it into a primary imagination and a secondary imagination. In rather vauge and nebulous terms, he defines the imagination as follows:

The primary imagination I hold to be the living power and prime agent of all human perception, and as a reception in the finite mind of the eternal act of creation in the infinite I AM. The secondary I consider as an echo of the former, coexisting with the conscious will, yet still as identical with the primary in the kind of its agency, and differing only in degree, and in the mode of its operation.

Coleridge's distinction between what he terms primary and secondary imagination has baffled many critics throughout the centuries, as many have argued that he does not sufficiently elaborate on the difference between the two different kinds of imagination. Primary imagination, as conceived by Coleridge, is about the impulse to write and create as dictated by overwhelming inspiration, whereas secondary imagination is about the conscious will of the writer to write and use their imagination to create. It is clear through his description of secondary imagination as an "echo of the former" that Coleridge believed primary imagination to be purer or more powerful.