the senses.

Imagination can have only a sensory basis.

The sensory education which prepares for the accurate perception of
all the differential details in the qualities of things, is therefore
the foundation of the observation of things and of phenomena which
present themselves to our senses; and with this it helps us to collect
from the external world the material for the imagination.

Imaginative creation has no mere vague sensory support; that is to
say, it is not the unbridled divagation of the fancy among images of
light, color, sounds and impressions; but it is a construction firmly
allied to reality; and the more it holds fast to the forms of the
external created world, the loftier will the value of its internal
creations be. Even in imagining an unreal and superhuman world, the
imagination must be contained within limits which recall those of
reality. Man creates, but on the model of that divine creation in
which he is materially and spiritually immersed.

In literary works of the highest order, such as the _Divina Commedia_,
we admire the continual recurrence to the mind of the supreme poet of
material and tangible things which illustrate by comparison the things
imagined:

As doves
By fond desire invited, on wide wings
And firm to their sweet nest returning home,
Cleave the air, wafted by their will along;
Thus issued from that troop where Dido ranks,
They, through the ill air speeding.
(Carey's translation of Dante's _Inferno_, Canto V.)

And as a man with difficult short breath
Forespent with toiling, 'scaped from sea to shore,
Turns to the perilous wide waste, and stands
At gaze; e'en so my spirit, that yet fail'd
Struggling with terror, turn'd to view the straits
That none hath passed and lived.
(Carey's translation of Dante's _Inferno_, Canto I.)

As sheep that step from forth their fold by one
Or pairs, or three at once; meanwhile the rest
Stand fearfully, bending the eye and nose
To ground, and what the foremost does, that do.
The others, gathering round her if she stops,
Simple and quiet, nor the cause discern;
So saw I moving to advance the first
Who of that fortunate crew were at the head,
Of modest mien, and graceful in their gait.
(Carey's translation of Dante's _Purgatorio_, Canto III.)

As though translucent and smooth glass