There's way too much to be said here for one short post, but a handful of points. First, As a straight, white male I'm pretty confident that there's a lot that I don't understand about what it's like to live in the country I live in (the US) as a woman, or as a Black person, or as a gay man, or transgender person, or as a lesbian or... This seems both unremarkable and important. It's unremarkable because we all are familiar with the fact that one's circumstances can sometimes make it easier to see or understand certain things. Lived experience does make a difference, and the difference it makes can be important. For example: I suspect that a great many of the people who put in place the "separate but equal" regime that finally began to crumble with Brown v. Board of Education were pretty clueless about what "separate but equal" was like for Black Americans and therefore, about whether "separate but equal" was even a serious possibility. That's hardly a shocking thing to say. ...

I agree with my colleague that "Only if A, then B" is not idiomatic English, and so it's hard to know what your teacher meant. In teaching logic over the years, I've seen many examples that take this form: "Only if A, B" — leaving the word "then" out. An English example might be the somewhat stilted but acceptable "Only if you're at least 18 are you eligible to vote." That's the same as saying "You are eligible to vote only if you're at least 18." And that's different from saying "If you're at least 18, you're eligible to vote." Saying "If you're at least 18, you're eligible to vote" means that there are no other qualifications needed; being 18 or older is enough. Saying "You're eligible to vote only if you're at least 18" allows that there may be other requirements as well, such as being a citizen. So if what your teacher meant was "Only if A, B," then perhaps my example shows that this isn't the same as "If A then B."

Philosophers are usually not the right people to ask for fallacy names. Most of us don't remember many of them, and aside from a handful (begging the question, for instance) seldom mention them by name. You mention the red herring fallacy here. That's probably good enough, but it's not any better than just noting that the response misses the point. If A says that taxing would be more effective than philanthropy and B says that philanthropy does some good, all A need say is "I agree: philanthropy does some good, but my point is that it's less effective than simply taxing people." A might be right or might be wrong, but what B says is irrelevant to the claim at issue, since A 's claim is entirely consistent with B 's reply. I notice this a lot on Quora. There's a whole sub-genre of questions in which people people describe a bit of reasoning gone wrong, and then ask for the name of the fallacy. Often the person has already done a good job of saying what's wrong. Sometimes...

The argument is valid. That's because in logic, we say that an argument is valid if it's impossible for the premises to be true and the conclusion false at the same time. If two statements A and If A then B really are true, then so is B . If both A and If A then B are false (or better, if at least one of them is), then the conclusion might be true or might be false, but the argument is still valid; the conclusion still follows. You seem to say that if we have no evidence for something, then it's false. But that's not right. Lots of things are true whether anyone knows them. (How many worms were there in the garden plot at noon yesterday? There's only one right answer, but no one happens to know it or even have evidence.) And things can turn out to be false even if we have serious evidence that they're true. And you seem to be saying that if the premises of an argument are false, the conclusion must be false too. But that's not right, and in particular it's not right even for valid...

The fallacy of composition is drawing conclusions about the whole from facts about the parts when the facts about the parts don't support the conclusion . Obvious case: every cell in my body weighs less than a pound. But that doesn't support the conclusion that I weigh less than a pound. The fallacy of composition is an informal fallacy: you can't tell whether it's been committed just by looking at the form of the inference while ignoring the content. In any case, the inference you're considering isn't a conclusion about a particular car—a whole—based on premises about its parts. It's a conclusion about all or most cars of a certain sort based on facts about some cars of that sort. This doesn't count as a part/whole relationship in the sense relevant for potential cases of the fallacy of composition. "Chevy cars" aren't a whole in the relevant sense. On the other hand, it would be hasty to generalize about Chevies based on a sample of two. So yes: hasty generalization. A footnote, however:...

The problem here, I think, is that there's no one answer to the question "What are the fundamental laws of logic?" We can do things in different ways, and things which are fundamental on some accountings will be derived on others. Let's assume that there is a definite answer to the question "What are the logical truths of classical logic?" (I'm using this as a proxy for "logical statements." If we want to expand it to include principles of inference, like modus ponens, that's okay too.) Note that the set of all such truths will be infinite, but that's okay. And to make "classical logic" well-defined, let's assume we mean truth-functional and first-order predicate logic, in which our first assumption is indeed correct. Then there are sets of rules and/or axiom schemes that provably allow the derivation of every logical truth thus understood. As just noted, there is no one way to so this, and the different ways won't contain the same axioms and/or rules. Even "the law of non-contradiction" will show...

There's a problem with your symbolization. The word "since" isn't a conditional. It's more like a conjunction, but better yet, we can treat it as simply giving us another premise. So in a slightly modified version of your notation, the argument would be N v D F → N D ∴ ¬F But from the premises as given, the conclusion won't be derivable. The reason is simple. You are assuming that if it's day it's not night and vice-versa. That may be part of the meaning of the words, but the symbols 'N' and 'D' aren't enough to capture it. The easiest fix is to treat "day" as "not night." That gives us N v ¬N F → N ¬N ∴ ¬F In this case, the first premise is a tautology and not needed. The argument is just a case of Modus Tollens. If you want something less trivial, you can drop the first premise and add a premise like this: D ↔ ¬N F → N D ∴ ¬F The first premise amounts to making the "v" exclusive. From there it's easy to complete a proof. A couple of extra comments. First, in the English version, you add a...

I'm sure that Stephen Maitzen will have useful things to say, but I wanted to chime on in this one. You have just given a perfectly consistent description of what actually happens in a simple polarization experiment that I use most every semester as a teaching tool. Classical logic handles this case without breaking a sweat. But there's another point. You've described the phenomenon in terms of light waves. That's fine for many purposes, but note that the wave version of the story of this experiment comes from classical physics, where (for the most part at least) there's no hint of logical paradox. The classical explanation for the result is that a polarizing filter doesn't just respond to a property that the light possesses. It also changes the characteristics of the wave. Up-down polarized light won't pass a left-right filter, but if we put a diagonal filter between the two, the classical story is that the intermediate filter lets the diagonal component of the wave pass, and when it does, the light...

There's a lot going on here. You begin this way: Given a particular conclusion, we can, normally, trace it back to the very basic premises that constitute it. If by "conclusion" you mean a statement that we accept on the basis of explicit reasoning, then we can trace it back to the premises we reasoned from simply because we've supposed that there are such premises. On the other hand, most of what we believe doesn't come from explicit reasoning. (I don't reason to the conclusion that I had a burrito for lunch. I just remember what I ate.) And even when it does, the premises don't usually constitute the conclusion. The easiest way to see this is to consider non-deductive reasoning. A detective may conclude that Lefty was the culprit because a number of clues point in that direction. Maybe a witness saw someone who looks like him; maybe he had a particular motive for the crime. But the clues don't constitute Lefty being the criminal; they merely make it likely. After all, even given all the...

I don't know the name, though I like "semantic bloating." In any case, a couple of observations. First, words mean what people use them to mean. Words in English mean what competent speakers use them to mean—or, at least, that's close enough for our purposes. Competent speakers of English don't use the word "cult" to refer to the whole human race. But the issue isn't really about the word. If your friend has a point, s/he ought to be able to make it by setting the word "cult" aside. What bothers us about the things we typically label cults is that they display a cluster of undesirable traits and tendencies. They make a rigid distinction between insiders and outsiders; they enforce membership conditions that alienate members from family and friends who mean them no harm; they insist on accepting dubious beliefs; they make it psychologically distressing for people to challenge or doubt those beliefs; they expect unquestioning obedience to the group's authority figures. All of these things show up in...