In executing this general plan, it was necessary first of all to
distinguish the imagination from our other faculties; and in the
next place to characterise those original forms or properties of
being, about which it is conversant, and which are by nature adapted
to it, as light is to the eyes, or truth to the understanding. These
properties Mr. Addison had reduced to the three general classes of
greatness, novelty, and beauty; and into these we may analyse every
object, however complex, which, properly speaking, is delightful to
the imagination. But such an object may also include many other
sources of pleasure; and its beauty, or novelty, or grandeur, will
make a stronger impression by reason of this concurrence. Besides
which, the imitative arts, especially poetry, owe much of their
effect to a similar exhibition of properties quite foreign to the
imagination, insomuch that in every line of the most applauded poems,
we meet with either ideas drawn from the external senses, or truths
discovered to the understanding, or illustrations of contrivance and
final causes, or, above all the rest, with circumstances proper to
awaken and engage the passions. It was, therefore, necessary to
enumerate and exemplify these different species of pleasure;
especially that from the passions, which, as it is supreme in the
noblest work of human genius, so being in some particulars not a
little surprising, gave an opportunity to enliven the didactic turn
of the poem, by introducing an allegory to account for the appearance.