On the nature of things (books 4 - 6)   

Unable now to conquer false with true;
And memory lies prone and languishes
In slumber, nor protests that he, the man
Whom the mind feigns to see alive, long since
Hath been the gain of death and dissolution.

And further, 'tis no marvel idols move
And toss their arms and other members round
In rhythmic time- and often in men's sleeps
It haps an image this is seen to do;
In sooth, when perishes the former image,
And other is gendered of another pose,
That former seemeth to have changed its gestures.
Of course the change must be conceived as speedy;
So great the swiftness and so great the store
Of idol-things, and (in an instant brief
As mind can mark) so great, again, the store
Of separate idol-parts to bring supplies.

It happens also that there is supplied
Sometimes an image not of kind the same;
But what before was woman, now at hand
Is seen to stand there, altered into male;
Or other visage, other age succeeds;
But slumber and oblivion take care
That we shall feel no wonder at the thing.

And much in these affairs demands inquiry,
And much, illumination- if we crave
With plainness to exhibit facts. And first,
Why doth the mind of one to whom the whim
To think has come behold forthwith that thing?
Or do the idols watch upon our will,
And doth an image unto us occur,
Directly we desire- if heart prefer
The sea, the land, or after all the sky?
Assemblies of the citizens, parades,
Banquets, and battles, these and all doth she,
Nature, create and furnish at our word?
Maugre the fact that in same place and spot
Another's mind is meditating things
All far unlike. And what, again, of this:
When we in sleep behold the idols step,
In measure, forward, moving supple limbs,
Whilst forth they put each supple arm in turn
With speedy motion, and with eyeing heads
Repeat the movement, as the foot keeps time?
Forsooth, the idols they are steeped in art,
And wander to and fro well taught indeed,-
Thus to be able in the time of night
To make such games! Or will the truth be this:
Because in one least moment that we mark-
That is, the uttering of a single sound-
There lurk yet many moments, which the reason
Discovers to exist, therefore it comes
That, in a moment how so brief ye will,
The divers idols are hard by, and ready
Each in its place diverse? So great the swiftness,
So great, again, the store of idol-things,
And so, when perishes the former image,
And other is gendered of another pose,
The former seemeth to have changed its gestures.
And since they be so tenuous, mind can mark
Sharply alone the ones it strains to see;