Is "no swans are black" a cleverly disguised double-negative?
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Original Question
Assume for the sake of this argument that all swans are white. One could then claim that no swans are black, or blue, or orange. Are these legitimate arguments in their own right, or are they simply clever ways to disguise the double-negative that no swans are not white? Is this an important logical distinction? If so, how does one guard against them?
Answers
3I would think by the same logic we can say anything is a cleverly disguised double negative. For example "no schools are open today" can also mean "no schools are not closed today." I could be missing your point and your concern here but I see no fallacy.
I agree with Dr. Bo: anything can be thought of as a double negative. The proposition P is true (or false ) when not not P is true (or false) and vice-versa. Are you asking if the use of double negatives can be used as a rhetorical devise? I guess you could convince a kid to stop lying. If you tell the kid to stop lying, he might think that you're imposing a rule and might rebel against it. Saying "if its not the truth, don't do it" sounds more like an advise.
(I am new to this site so I hope this is the correct place to post my answer, if not please feel free to let me know)
I think it depends on the person who is saying the quote in question, that is, “no swans are are black” and the context of the use of such a phrase.
1.) this can be the honest opinion of someone who actually believes that there are no swans that are the color black. In this case the double-negative would not be intended, it would just be due to the way in which a person speaks without knowing it is incorrect grammar.
2.) this can also be a clever way for someone to introduce a double-negative without the person spoken to realizing it is a double-negative. In this case, it would be to convince someone of a false truth to persuade them for an intended purpose, to trick them, to win an argument, or for some other reason.
I believe a way to guard against such a phrase would be to respond with a question that counters the force of the double-negative, as an example,
“no swans are black”
“but are all swans white?”
I think it depends on the person who is saying the quote in question, that is, “no swans are are black” and the context of the use of such a phrase.
1.) this can be the honest opinion of someone who actually believes that there are no swans that are the color black. In this case the double-negative would not be intended, it would just be due to the way in which a person speaks without knowing it is incorrect grammar.
2.) this can also be a clever way for someone to introduce a double-negative without the person spoken to realizing it is a double-negative. In this case, it would be to convince someone of a false truth to persuade them for an intended purpose, to trick them, to win an argument, or for some other reason.
I believe a way to guard against such a phrase would be to respond with a question that counters the force of the double-negative, as an example,
“no swans are black”
“but are all swans white?”
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