Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     In these affairs
We wish thee also well aware of this:
The atoms, as their own weight bears them down
Plumb through the void, at scarce determined times,
In scarce determined places, from their course
Decline a little- call it, so to speak,
Mere changed trend. For were it not their wont
Thuswise to swerve, down would they fall, each one,
Like drops of rain, through the unbottomed void;
And then collisions ne'er could be nor blows
Among the primal elements; and thus
Nature would never have created aught.
     But, if perchance be any that believe
The heavier bodies, as more swiftly borne
Plumb down the void, are able from above
To strike the lighter, thus engendering blows
Able to cause those procreant motions, far
From highways of true reason they retire.
For whatsoever through the waters fall,
Or through thin air, must quicken their descent,
Each after its weight- on this account, because
Both bulk of water and the subtle air
By no means can retard each thing alike,
But give more quick before the heavier weight;
But contrariwise the empty void cannot,
On any side, at any time, to aught
Oppose resistance, but will ever yield,
True to its bent of nature. Wherefore all,
With equal speed, though equal not in weight,
Must rush, borne downward through the still inane.
Thus ne'er at all have heavier from above
Been swift to strike the lighter, gendering strokes
Which cause those divers motions, by whose means
Nature transacts her work. And so I say,
The atoms must a little swerve at times-
But only the least, lest we should seem to feign
Motions oblique, and fact refute us there.
For this we see forthwith is manifest:
Whatever the weight, it can't obliquely go,
Down on its headlong journey from above,
At least so far as thou canst mark; but who
Is there can mark by sense that naught can swerve
At all aside from off its road's straight line?
     Again, if ev'r all motions are co-linked,
And from the old ever arise the new
In fixed order, and primordial seeds
Produce not by their swerving some new start
Of motion to sunder the covenants of fate,
That cause succeed not cause from everlasting,
Whence this free will for creatures o'er the lands,
Whence is it wrested from the fates,- this will
Whereby we step right forward where desire
Leads each man on, whereby the same we swerve
In motions, not as at some fixed time,
Nor at some fixed line of space, but where
The mind itself has urged? For out of doubt
In these affairs 'tis each man's will itself
That gives the start, and hence throughout our limbs
Incipient motions are diffused. Again,
Dost thou not see, when, at a point of time,
The bars are opened, how the eager strength
Of horses cannot forward break as soon
As pants their mind to do? For it behooves
That all the stock of matter, through the frame,
Be roused, in order that, through every joint,
Aroused, it press and follow mind's desire;
So thus thou seest initial motion's gendered
From out the heart, aye, verily, proceeds
First from the spirit's will, whence at the last
'Tis given forth through joints and body entire.
Quite otherwise it is, when forth we move,
Impelled by a blow of another's mighty powers
And mighty urge; for then 'tis clear enough
All matter of our total body goes,
Hurried along, against our own desire-
Until the will has pulled upon the reins
And checked it back, throughout our members all;
At whose arbitrament indeed sometimes
The stock of matter's forced to change its path,
Throughout our members and throughout our joints,
And, after being forward cast, to be
Reined up, whereat it settles back again.
So seest thou not, how, though external force
Drive men before, and often make them move,
Onward against desire, and headlong snatched,
Yet is there something in these breasts of ours
Strong to combat, strong to withstand the same?-
Wherefore no less within the primal seeds
Thou must admit, besides all blows and weight,
Some other cause of motion, whence derives
This power in us inborn, of some free act.-
Since naught from nothing can become, we see.
For weight prevents all things should come to pass
Through blows, as 'twere, by some external force;
But that man's mind itself in all it does
Hath not a fixed necessity within,
Nor is not, like a conquered thing, compelled
To bear and suffer,- this state comes to man
From that slight swervement of the elements
In no fixed line of space, in no fixed time.