Lucretius: On the Nature of the Universe, translated by Ronald Melville, Oxford World’s Classics, Oxford University Press, 1997

Book 4, lines 469-521:

  Now here’s another thing: if someone thinks
That nothing is known, he does not even know
Whether that can be known, since he declares
That he knows nothing.
Therefore I will spare
To argue a case against a man like this
Who has put his head where his feet ought to be.
And yet, if I were to grant that he does know, then
I ask him this: since you could see no truth
In anything before, how do you know
What it is to know, and what again not to know?
What gave you the idea of true and false,
What proves to you that there’s a difference,
That the doubtful and the certain are not the same?
You will find that it is from the senses
In the first place that the concept of truth has come,
And that the senses cannot be refuted.
For some standard must be found of greater credit
Able of itself to refute false things with true.
And what can be held to tell the truth more clearly
Than the senses? or shall reasoning derived
From false senses prevail against those senses
Being itself wholly derived from them?
Unless they are true, all reasoning is false.
Will the ear be able to convict the eye?
Or the touch the ear? Or taste refute the touch,
Or nose confound it or eye discredit it?
Not so, I think. For each has its own force
And separate power, so it needs must be
That softness and cold or heat and colour each
Is separately perceived and separately
We see whatever is involved in colour.
The taste in our mouth has its separate power, and smells
Have separate birth, and sounds. So it must be
That one sense never can refute another
Nor can they possibly convict themselves
Since each must always equally be trusted.
Accordingly whatever at any time
Has seemed to the senses to be true, is true.
And if reason cannot explain the cause
Why objects seen as square close to at a distance
Seem round, yet it is better that a man
Lacking reason should give a faulty explanation
Than to let slip from your hands in any way
Your grip upon the obvious, and break
The trust upon which all depends, and tear up
All the foundations on which life is built.
For not only would all reason come to ruin,
Life itself also would at once collapse,
Unless you dare to place trust in your senses,
Avoiding precipices and such things
As must be shunned, and follow the contrary.
Believe me, all that array of words is vain
That has been massed and deployed against the senses.
Lastly, in a building, if the ruler is crooked
And the square is faulty and misses the straight line
And the level is even slightly unbalanced,
The whole house then will of necessity
Be wrongly constructed and be falling over,
Warped, sloping, leaning forward, leaning back,
All out of proportion, so that some parts seem
Ready to collapse, and the whole destined to fall,
A victim to the first false measurements.
So your reasoning about things must be false and warped
Whenever it is based upon false senses.

A. A. Long and D. N. Sedley, The Hellenistic Philosophers. Volume 1: Translations of the Principal Sources with Philosophical Commentary, Cambridge University Press, 1987

pp. 78-79, Section 16 A:

Lucretius, De Rerum Natura, Book IV, lines 469-499

  1. Now, if someone thinks that nothing is known, one thing he doesn’t know is whether that can be known, since he admits to knowing nothing. I shall therefore not bothet to argue my case against this man who has himself stood with his own head in his footprints,
  2. And anyway, even allowing that he knows this, I’ll still ask him: given that he has never before seen anything true in the world, from where does he get his knowledge of what knowing and not knowing are? What created his preconception of true and false? And what proved to him that doubtful differs from certain?
  3. You will find that the preconception of true has its origin in the senses, and that the senses cannot be refuted.
  4. For something of greater reliability must be found, something possessing the intrinsic power to convict falsehoods with truths. Well, what should be considered to have greater reliability than the senses?
  5. Will reason have the power to contradict them, if it is itself the product of false sensation? For reason is in its entirety the product of the senses, so that if the senses are not true all reason becomes false as well.
  6. Or will the ears have the power to confute the eyes, and touch to confute the ears? Or again, will this sense of touch be denounced by the mouth’s taste, confuted by the nose, or convicted by the eyes? That is not, in my view, the way things are. For each has its own separate capacity and its own power, thus making it necessary that sensing what is soft, cold or hot be a separate operation from sensing the various colours of things and seeing whatever properties regularly accompany colours. Likewise the mouth’s taste has a separate power, the recognition of smells is separate, and separate again that of sounds. It necessarily follows that the senses cannot convict each other.
  7. Nor, again, will they be able to confute themselves, since all will always have to be considered of equal reliability.
  8. Hence whatever impression the senses get at any time is true.
  9. Even if reason fails to explain why things which proved square when close up seem round at a distance, it is nevertheless better, when one’s reason proves inadequate, to give wrong explanations of the respective shapes, than to let the self-evident slip from one’s grasp and thus to violate the primary guarantee and shake the entire foundations on which life and survival rest.
  10. For not only would all reason cave in, but life itself would instantly collapse, if you lost the confidence to trust your senses, and to avoid precipices and other such hazards while aiming towards things of the opposite kind.
  11. Hence you will find that the entire battalion of words which has been marshalled and armed against the senses is futile.
  12. Lastly, just as in a building, if the yardstick is defective at the outset, if the set square is misleading for lack of straight edges, and if the level has the slightest wobble anywhere in it, the inevitable result is that the whole house is made wrongly — crooked, distorted, bulging backwards and forwards, misproportioned — so much so that some parts seem already determined to cave in, and do cave in, all betrayed by false initial criteria, so too you will find that any account of the world must be distorted and false if it is based upon the falsity of the senses.

Lucretius, De Rerum Natura 4.469-521:1

  Denique nil sciri siquis putat, id quoque nescit
an sciri possit, quoniam nil scire fatetur.
hunc igitur contra minuam contendere causam,
qui capite ipse suo in statuit vestigia sese.
et tamen hoc quoque uti concedam scire, at id ipsum
quaeram, cum in rebus veri nil viderit ante,
unde sciat quid sit scire et nescire vicissim,
notitiam veri quae res falsique crearit
et dubium certo quae res differre probarit.
invenies primis ab sensibus esse creatam
notitiem veri neque sensus posse refelli.
nam maiore fide debet reperirier illud,
sponte sua veris quod possit vincere falsa.
quid maiore fide porro quam sensus haberi
debet? an ab sensu falso ratio orta valebit
dicere eos contra, quae tota ab sensibus orta est?
qui nisi sunt veri, ratio quoque falsa fit omnis.
  An poterunt oculos aures reprehendere, an aures
tactus? an hunc porro tactum sapor arguet oris,
an confutabunt nares oculive revincent?
non, ut opinor, ita est. nam seorsum cuique potestas
divisast, sua vis cuiquest, ideoque necesse est
et quod molle sit et gelidum fervensve videre
et seorsum varios rerum sentire colores
et quae cumque coloribus sint coniuncta necessest.
seorsus item sapor oris habet vim, seorsus odores
nascuntur, seorsum sonitus. ideoque necesse est
non possint alios alii convincere sensus.
nec porro poterunt ipsi reprehendere sese,
aequa fides quoniam debebit semper haberi.
proinde quod in quoquest his visum tempore, verumst.
  Et si non poterit ratio dissolvere causam,
cur ea quae fuerint iuxtim quadrata, procul sint
visa rutunda, tamen praestat rationis egentem
reddere mendose causas utriusque figurae,
quam manibus manifesta suis emittere quoquam
et violare fidem primam et convellere tota
fundamenta quibus nixatur vita salusque.
non modo enim ratio ruat omnis, vita quoque ipsa
concidat extemplo, nisi credere sensibus ausis
praecipitisque locos vitare et cetera quae sint
in genere hoc fugienda, sequi contraria quae sint.
illa tibi est igitur verborum copia cassa
omnis, quae contra sensus instructa paratast.
  Denique ut in fabrica, si pravast regula prima,
normaque si fallax rectis regionibus exit,
et libella aliqua si ex parti claudicat hilum,
omnia mendose fieri atque obstipa necessu est
prava cubantia prona supina atque absona tecta,
iam ruere ut quaedam videantur velle, ruantque
prodita iudiciis fallacibus omnia primis,
sic igitur ratio tibi rerum prava necessest
falsaque sit, falsis quae cumque ab sensibus ortast.