ask a question

recent responses

all topics

info

⚲

Language
Logic

A statement P about a single element in a dual or multiple set does not seem to logically exclude P applying equally to other elements in the set; yet we often talk as though "P is true of X" implies "P is not true of Y (or Z)", when X, Y, and Z all belong to some grouping. For example, take "Men work to support their families". Does this logically imply that women do not work to support their families? What about "African Americans suffer from discrimination"? Does this logically imply that Asian Americans, Hispanic Americans and white Americans (among other racial groupings) do not suffer from discrimination? Such objections are often raised in discourse. Given (x, y), "P is true of X" is thought to imply "P is not true of Y", or "Not-P is true of Y". If there is no logical exclusion above, what are these objections targeting? Is it a question of salience, rather than logic?

Thank you for your good question! Answering questions of this general type has been a big concern of the field of philosophy of language for the last few decades. One way of starting to understand where this tradition is coming from, is to distinguish between the literal meaning of a sentence, and the meaning that a speaker using that sentence is normally thought to convey. So suppose that you often has unkempt hair. One day you show up with nicely combed hair and I remark, "Your hair is combed!" Now it will be natural to take me to be *suggesting* that your hair is normally not tidy. But this is no part of the literal meaning of the sentence. If it were, then I'd contradict myself by saying, "Your hair is combed, though of course it is normally tidy." This might be an odd things to say, but it isn't a self-contradiction like, "Bob is a bachelor, but he is married." So we can distinguish between what a sentence usually means and what a person uttering that sentence might be conveying,...
Language
Logic

Hi. Take the following syllogism : John believes that green people should be killed. Mushmush is a green person, a neighbour of John. ====================== Thus, John believes that Mushmush should be killed. Formally, the argument seems valid. However, in reality it doesn't work. A persona can believe that all people with quality X should be killed, but not think it about a specific person he knows. So is there a logical contradiction here? What happens? Thank you, Sam

Whoa! With all due respect to Professor Nahmias, he is mistaken. The syllogism is NOT valid and here is why. Propositions that are "in the scope" of words like belief can't be manipulated while preserving validity. So while, Green people should be killed. Mushmush is a green person. ergo, Mushmush should be killed is valid, embedding the first premise in the scope of belief ('John believes that green people should be killed') will destroy the argument's validity. Words like 'believes' (and related ones such as 'knows', 'wants', 'fears') create what is known as opaque contexts, in which inferences that would otherwise be valid are no longer valid. The reason is that what a person believes (knows, wants, fears) depends not only on what is implied by the propositions he believes, but also on whether he *realizes* that these things are implied. Alas, we are all too often unaware of what is implied by the things that we believe. The point here has been discussed in detail by...
Logic
Mind

Many claims about what is possible or logical seem to rest on what is conceivable to the human mind. But what reason do we have to believe that there's any link between the way our minds work and the way things actually are?

Thank you for your question. For a long while in the history of philosophy it was thought that what was conceivable was a good indication of what was possible. Descartes is a good example of this way of thinking, though he was careful to require that not any old conceiving of a thing showed it to be possible. Rather he required that the conceiving had to be "clear and distinct", meaning roughly that it had to pass the most stringent standards we can muster to make sure the conceiving is coherent (i.e., not subtly self-contradictory). In the middle of the 20th century this methodology began to break down. For instance, in the Sixties Hilary Putnam distinguished between concepts and properties, making clear that our concepts of things like gold may not reveal its true properties. Similarly, Kripke's notion a decade later of "natural kinds" made room for the possibility that what is "metaphysically possible" may not correspond to that is conceivable. This issue is still a topic of intense...
Logic

I’m familiar with syllogistic arguments, but hardly an expert. In a recent debate about logical fallacies, I made the following points. So-called logical fallacies do not apply to inherently sound arguments (much as, for example, libel isn’t libel if the statement is true). Therefore, it is logically sound to "appeal" to numbers or to authorities IF the majority or the authority being cited: (1) has legitimate expertise on the topic (e.g., a doctor, not a mechanic on a medical matter); (2) is cited only in the area of its expertise (e.g., don't cite computer programmers on a biological question); and (3) the subject-matter experts generally agree on the statement (as, for instance, most oncologists agree that smoking is a cause of lung cancer). In other words, it is perfectly logical to accept as valid the consensus of lung-cancer researchers that smoking is a leading cause of lung cancer. I may have phrased my case ineptly, but I wonder if my argument is correct, or at least on the right track. Thank...

Thanks for your question. According to the standard technical definition of a sound argument (defined as a valid argument with all true premises, and where a valid argument is defined as an argument such that there is no way for the conclusion to be false while all the premises are true), it is possible for an argument to be sound but fallacious. For instance, we would normally call a circular argument (where the conclusion appears as one of the premises) fallacious, but according to the definition of a sound argument I just gave it is obviously sound. Second, appealing to authorities as you describe in your question may be rational, justified, and the like, but it is not sound if put in the form: "The authorities claim that P, therefore P", or something slightly less trivial. Obviously, and alas, all the authories might agree on an issue, and back up their view with evidence, and still be wrong. Now this might just show that the standard definition of a sound argument as used in...