A question from T.W. got me thinking about how to look at the validity of the senses, and for a cite from the texts to make that issue clear. We talk all the time about the issue of how to use the senses, and that an individual sensation can be "wrong to the facts" but still reported "honestly" and from that perspective be "true" ("true" not in the sense of being "accurate" but in the sense of "honest").
The basic point is that some sensations convey information that is distorted by intervening factors, and some sensations convey more detailed information. When we see the tower at a distance, the distance distorts the image, and we think it looks round when it is really square. Distance, fog, and other intervening issues can distort the images before they get to us. As in DeWitt's analogy to a witness in court, the eyes are testifying "truly" according to what they see, but what they see may not be in accord with the actual facts.
But there is a deeper issue: "How do we know that the senses are reliable in general"? Why should we have confidence that we are not living in a simulation? Is there some method of logical proof that will allow us to validate that the senses are reliable?
In a similar way, we can ask how Epicurus could be so sure that there are no supernatural gods. Is it because he has constructed a logical argument, based on "anticipations" or something else, that the "gods" have no supernatural powers? I would say "no" -- I would bet that if Epicurus were here, he would say that he used logical deduction to bolster his conclusion, but that the more fundamental starting point by which he reached the conclusion in the first place was **observation**. As is made clear in both the letter to Herodotus and in Lucretius' De Rerum Natura, the starting point of the argument is the observation that nothing comes from nothing, followed closely by the second observation that nothing goes to nothing. it is by chain reasoning that starts at this single point that all of the system is based, and on which all of the system would fall if these points were proved to be incorrect.
So the question is then how do we know that our observations should be believed? Is there a clear reference in the Epicurean texts to establish why the senses, which sometimes produce sensations that are obviously distorted, should be given our confidence? I think here is such a text reference, from Diogenes Laertius, within the following passage:
"Nor is there anything which can refute sensations or convict them of error: one sensation cannot convict another and kindred sensation, for they are equally valid; nor can one sensation refute another which is not kindred but heterogeneous, for the objects which the two senses judge are not the same; nor again can reason refute them, for reason is wholly dependent on sensation; nor can one sense refute another, since we pay equal heed to all. And the reality of separate perceptions guarantees the truth of our senses. But seeing and hearing are just as real as feeling pain."
This is the translation at Epicurus.net, and the key sentence is "The reality of separate perceptions guarantees the truth of the senses."
Hicks in the Loeb edition translates: "And the reality of separate perceptions guarantees the truth of our senses."
But there are less clear translations:
Epicurus Reader (Inwood / Gerson): "And the fact of our awareness of sense-perceptions confirms the truth of the sense-perceptions." This one seems circular and almost nonsensical. The fact that we are aware of them is what confirms their truth? I hardly think that makes sense or that Epicurus could have asserted this.
Yonge: "Reality and the evidence of sensation establish the certainty of the senses; ...." Again, circular at best.
Bailey: "Again, the fact of apperception confirms the truth of the sensations." it frequently appears to me that Bailey translates in a way geared to produce a meaning he prefers. Here he uses an obscure word ("apperception") that seems unlikely to have been the style used in the original Greek by a philosopher who was accused of being overly plain.
Comparing all these translations, especially Epicurus.net and Hicks, I suggest this passage means that the fact the reason for our confidence in the senses is that through repeated observations over time, under the same conditions, we receive the same result. It is that repetition over time which is the guarantee that the senses as a faculty are valid and to be trusted.
It is clear Epicurean theory that it is impossible by abstract reason or theoretical logic or by divine revelation or by any other alleged method to "go behind" the senses and ultimately prove them to be worthless. As Epicurus says, each sensation is relayed without opinion, so each sensation is entitled to equal respect as being unbiased. But over time, and through many observations under separate conditions, it is possible to compare them with each other and see that the information they are providing converges toward a single conclusion.
It is therefore our experience that the sugar we taste is sweet under most every condition in which we taste it; that water feels "wet" under most every condition we feel it; that fire feels warm under most ever condition we feel it, etc. which gives us confidence that the senses are to be trusted. Yes we understand that disease can alter our sense of taste or touch, or that temperature can change the consistency of water, and that all sorts of distortions in observation can occur, but it is the reality that over time separate perceptions converge toward a limit, and that a picture emerges that is consistent over time and conditions, on which our confidence must rest.
There's no way to "reason" ourselves to the conclusion that the senses are valid (or invalid) without reliance on the senses themselves as data to consider. Repeated observation is the ultimate basis for confidence in all areas of Epicurean reasoning.
Should we see with our own eyes a series of humans come back to life from the dead at the command of Jesus or his disciples, we would immediately become Christians.
Should we see with our own eyes that dead warriors are rewarded for eternity with some large number of sexually attractive playthings, we would immediately (or most likely) choose to become Islamic activists.
Should we learn in the future through our rockets and telescopes that indeed everything revolves around the earth, we would immediately reevaluate our perspective on religion and start looking for the prime movers or the personal saviors or the Yahwehs who made humanity the center around which all things revolve.
But none of those things have ever been observed by us, nor do we have reason to believe that they will be observed in the future, or that those in the past who made such assertions should be given more credibility our own experiences.
All of this leads to the ultimate point that we should not look for justification for our conclusions in abstract theoretical "logic" or "reason." Logic and reason are tools, and cannot function without our natural faculties of perception. The thing in which to ground our confidence that our conclusions are correct - the guarantee of the reliability of our senses - is the reality of separate perceptions. It is the reality that separate perceptions, which again and again over time, produce the same results under the same circumstances, that is the basis of our confidence that the process of thinking based on factual experience is valid.
So it seems to me that even though this brief passage may be a summary by Diogenes Laertius, and not a direct quote from Epicurus, it probably stands up there with "nothing comes from nothing" and "nothing goes to nothing" in significance for us to remember:
"The reality of separate perceptions guarantees the truth of the senses" or "The reality of separate perceptions is the guarantee of the truth of the senses."