"used in auxiliary function to express what is probable or expected" (Merriam-Webster)-0+ wrote: ↑July 18th, 2021, 1:37 amAn absence of evidence for p is an absence of evidence. How does zero evidence for p become positive evidence for ~p?
What does 'should' mean in "there should be evidence of p"?
In this sense, for example, if there is milk in your fridge, there should be perceptual evidence for it that you can obtain by opening its door and looking inside, since milk is easily visible stuff. And if you do so (thoroughly) without finding any (positive) perceptual evidence for the presence of milk, then this is (negative) perceptual evidence for the absence of milk, and you are thereby justified in believing that there is no milk in your fridge.
The central form of evidence in empirical science is perceptual evidence in the form of perceptual experience; and there's a distinction between things or facts which are perceptually accessible (in practice or in principle at least) and ones which are not. Of course, there cannot be any perceptual evidence for perceptually inaccessible, imperceptible things or facts; but imperceptibility and a corresponding lack of perceptual evidence don't entail nonexistence, since—pace George Berkeley—it is not the case that being is being perceived.-0+ wrote: ↑July 18th, 2021, 1:37 amIf, for a particular p, "p is true" implies "there is evidence for p", then zero evidence for p implies p is not true.
Does this logical conclusion based on zero evidence and the precondition qualify as positive evidence for ~p? Accepting that p is true could be based on evidence or based purely on logic without any evidence. Does logic qualify as evidence or is logic beyond evidence?
What is needed for "p is true" to imply "there is evidence for p"?
Perhaps this depends on what qualifies as evidence?
So the absence of evidence for a thing or fact is evidence for its absence if and only if it is perceptually accessible (directly or indirectly at least), and no perceptual evidence for it has been found—provided the search for evidence was performed non-superficially, painstakingly, i.e. with great care and attention.
For example, if there is milk in your fridge, but it is "magic milk" that becomes invisible as soon as you open its door, then the absence of visual evidence for it is not evidence for its absence if you know that it becomes invisible every time the door is opened. For then you cannot expect there to be visual evidence for it.
There is no perceptual evidence for something before somebody had some perceptual experience of it. For instance, I have no visual or auditory evidence for there being a fly in my living room unless I actually see or hear a fly in my living room. My seeing or hearing (or my seeming to see or hear) a fly is my evidence for there being a fly.-0+ wrote: ↑July 18th, 2021, 1:37 amIf p is a statement regarding the physical existence of X, then if X exists it may be assumed there will be some kind of indication in the universe that X exists which could qualify as evidence. Does this "evidence" need to be discovered and/or possessed before it qualifies as evidence?
But the term "evidence" isn't always used to refer to perceptual/experiential evidence (in the form of perceptual experience). Especially in the legal context, physical items or signs are called evidence, and such physical evidence exists before it is perceived by somebody (as opposed to mental evidence or "phenomenal evidence" in the form of perceptual experience):
"When one compares philosophical accounts of evidence with the way the concept is often employed in non-philosophical contexts, however, a tension soon emerges. Consider first the kinds of things which non-philosophers are apt to count as evidence. For the forensics expert, evidence might consist of fingerprints on a gun, a bloodied knife, or a semen-stained dress: evidence is, paradigmatically, the kind of thing which one might place in a plastic bag and label ‘Exhibit A’. Thus, a criminal defense attorney might float the hypothesis that the evidence which seems to incriminate his client was planted by a corrupt law enforcement official or hope for it to be misplaced by a careless clerk. For an archaeologist, evidence is the sort of thing which one might dig up from the ground and carefully send back to one's laboratory for further analysis. Similarly, for the historian, evidence might consist of hitherto overlooked documents recently discovered in an archive or in an individual's personal library. Reflection on examples such as these naturally suggests that evidence consists paradigmatically of physical objects, or perhaps, physical objects arranged in certain ways. For presumably, physical objects are the sort of thing which one might place in a plastic bag, dig up from the ground, send to a laboratory, or discover among the belongings of an individual of historical interest."
In order have conclusive evidence for absence of X in Y, Y (eg, 51 cards on the table) needs to be finite, John's examination of Y needs to be exhaustive (he needs to have full access to Y and not leave any card unturned) and he needs to be able to tell the difference between X (Queen of Hearts) and ~X.[/quote]-0+ wrote: ↑July 18th, 2021, 1:37 amIf Mary places 51 playing cards face down on a table and says to John, "p is: one of these cards is the Queen of Hearts", it could be argued: if p is true then there is evidence of p on the table; John is just unable to view this evidence.
Initially John only sees 51 cards face down on the table. He has no evidence for p and no evidence for ~p. Relative to his lack of evidence, p and ~p are both possible. What can he conclude?
If John turns a card over, this reveals something. This provides him with some evidence. If this card is the Queen of Hearts, this is conclusive evidence for p. If this is another card then this may provide a little bit of evidence for ~p.
If he turns 50 cards over and none of these are the Queen of Hearts, this may provide a lot of evidence for ~p. If p is true, the chances are he would have uncovered conclusive evidence for this by now. But one card remains unturned. This may or may not be the Queen of Hearts. How can he usefully calculate the probability that p is true (or not true) at this stage?
If he turns over the 51st card and this is also not the Queen of Hearts, he may finally have conclusive evidence for ~p (assuming no card trickery).
If John knows Mary didn't lie, he knows (after having turned over 50 cards) that the 51st card is the Queen of Hearts before turning it over, since there is no other possibility. He doesn't know this in advance if he doesn't know whether Mary lied or not.
As I already remarked above, the search for evidence must be performed painstakingly so as not to make the mistake of failing to notice evidence that is there.
Of course, if the search area is the whole universe, then we'll never be justified in claiming e.g. that there is nowhere evidence for extraterrestrial life; and then we'll never be justified in claiming that there is no extraterrestrial life anywhere in the universe.
That's the good old epistemic question of other minds/consciousnesses: I know I am conscious, but how do I know whether you are too?-0+ wrote: ↑July 18th, 2021, 1:37 amIf John is not able to turn over any cards, he may not be able to obtain any evidence of p or ~p. However, if Mary says, "I know what the cards are; all the evidence you need is in my mind if you can access this", how can John access this evidence? If Mary is a robot, he may be able to access her internal data. If Mary is human he may able to intercept and decode her brain waves.
If Mary says, "p is: I, Mary, have phenomenal consciousness", how can John begin to obtain evidence for p, or evidence for ~p?
Other Minds: https://plato.stanford.edu/entries/other-minds/