He Who Says That Nothing Can Be Known Knows Nothing

1. Explanation

• The second poisonous doctrine that Epicurus identified is known to us today as Radical Skepticism. Skeptics hold that nothing in life can be known with confidence. The Skeptics of Epicurus' time argued, primarily due to their contention that the senses cannot be trusted, that we can never be certain of anything, and at most some things are "probable." Even something as obvious as the expectation that if you jump off a canyon wall you will fall to your death is not certain to such philosophers, it is merely "probable."
• Epicurus saw that this confidence-destroying doctrine suffers much the same flaw as Determinism - it is self-contradictory nonsense. Anyone who is ridiculous and absurd enough to advocate that "nothing can be known" is taking you for a fool, because he expecting you to accept that he knows that "nothing can be known." Epicurus held that that such arguments should not be taken seriously, any more than you should seriously accept the argument from a living person that it would be better never to have been born.
• Lucretius spoke for Epicurus in writing: " Again, if any one thinks that nothing is known, he knows not whether that can be known either, since he admits that he knows nothing. Against him then I will refrain from joining issue, who plants himself with his head in the place of his feet. And yet were I to grant that he knows this too, yet I would ask this one question; since he has never before seen any truth in things, whence does he know what is knowing, and not knowing each in turn, what thing has begotten the concept of the true and the false, what thing has proved that the doubtful differs from the certain? [Book 4:469]

2. Citations

1. Lucretius 4:469
   1. [469] Again, if any one thinks that nothing is known, he knows not whether that can be known either, since he admits that he knows nothing. Against him then I will refrain from joining issue, who plants himself with his head in the place of his feet. And yet were I to grant that he knows this too, yet I would ask this one question; since he has never before seen any truth in things, whence does he know what is knowing, and not knowing each in turn, what thing has begotten the concept of the true and the false, what thing has proved that the doubtful differs from the certain?
2. Diogenes of Oinoanda, Fragment 5
   1. Smith: "Now Aristotle and those who hold the same Peripatetic views as Aristotle say that nothing is scientifically knowable, because things are continually in flux and, on account of the rapidity of the flux, evade our apprehension. We on the other hand acknowledge their flux, but not its being so rapid that the nature of each thing [is] at no time apprehensible by sense-perception. And indeed [in no way would the upholders of] the view under discussion have been able to say (and this is just what they do [maintain] that [at one time] this is [white] and this black, while [at another time] neither this is [white nor] that black, [if] they had not had [previous] knowledge of the nature of both white and black."

3. Notes

1. Major Implications
   1. Radical skepticism is self-contradictory nonsense.
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