What fallacy is it ? hasty generalization or begging the question ? Is it really a fallacious argumnet or a valid one ? Premise1- If A is true, then B is true. Premise 2- A is true. Conclusion- B is true. We have no empirical evidence for supporting P1 and P2 therefore both are false. Since 1 or more than 1 premise is false, the conclusion will always be false. A guy argues that it is a valid argument. On the other hand, I say it is not a valid argument. I don't know which informal fallacy it is. Does this argument contain really a fallacy or the other guy is right ?

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...

What fallacy is being committed here: I owned two Chevy cars – a Cruze and a Malibu – and they gave me nothing but trouble. The choke and the batteries froze up and the clutches went out on both cars. They were always in the shop. Chevy’s are poorly constructed and should be avoided. What fallacy does this person commit? fallacy of hasty generalization or fallacy of composition? It is difficult to tell if the argument assumes that parts of the Chevy car are troublesome (batteries, clutch etc.) therefore the whole Chevy car is poorly constructed making this a composition fallacy or if the person has observed a small amount of Chevy cars and made a generalization about the whole of Chevy cars which in this case it would be a hasty generalization fallacy. These fallacies are hard to tell apart and a little confusing.

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:...

Is it - must there be - possible to track all logical statements back to the fundamental laws of logic ( the law of identity, the law of non-contradiction, etc.) when it comes to "classical logic"? Are all logic derived from these fundamental laws?

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...

how would i use natural deduction to prove this argument to be correct? Its always either night or day.There'd only be a full moon if it were night-time. So,since it's daytime,there's no full moon right now. i have also formalized the argument using truth functional logic i'm not sure if it is completely correct though and would much appreciate the help. symbolization key: N: night D: day Fm: full moon Nt: night time Dt: day time ((N V D) , (Fm → Nt) , (Dt → ¬Fm))

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...

In an answer to a question about logic, Prof Maitzen says he is unaware of any evidence that shows classical logic fails in a real-life situation. Perhaps he has never heard of an example from physics that shows how classic logic does not work in certain restricted situations? A polarizing filter causes light waves that pass through it to align only in one direction (e.g., up-down or left-right). If you have an up-down filter, and then a left-right filter behind it, no light gets through. However, if you place a filter with a 45 degree orientation between the up-down and left-right filter, some light does get through. It seems to me that classic logic cannot explain this real-world result. Thanks!

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...

Given a particular conclusion, we can, normally, trace it back to the very basic premises that constitute it. The entire process of reaching such a conclusion(or stripping it to its basic constituents) is based on logic(reason). So, however primitive a premise may be, we don't seem to reach the "root" of a conclusion. Do you believe that goes on to show that we are not to ever acquire "pure knowledge"? That is, do you think there is a way around perceiving truths through a, so to say, prism of reasoning, in which case, nothing is to be trusted?

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...

Hello! I have a question about a particular line of reasoning in a debate that, to me, only leads to a "do I care" conclusion. I have now encountered this reasoning in several debates and can't think of a better conclusion. There must be a name for this that I am not aware of. Most recently this happened in a debate about cults. We were chugging along on the topic of cults and what gets something labeled as a cult vs say a religion or a tribe or, more universally, just humanity. The conclusion, again to me, was that when you expand the definition of "cult" so far out, yes, the entire human race can be labeled a cult. That is to say that under that definition of the word "cult" everything can be labeled a cult and the only conclusion is "do I care". This did not help my friend who wishes to avoid all cults but seemingly proved they were in a cult called the human race. Is there a name for this type of semantic bloating? Is this perhaps a long established logical fallacy I'm not aware of?? Regards.

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...

Lately, I have been hearing many arguments of the form: A is better than B, therefore A should be more like B. This is despite B being considered the less desirable option (often by the one posing the argument). For example: The poor in our country have plenty of food and places to live. In other countries, the poor go hungry and have little to no shelter. It is then implied that the poor in our country should go hungry and have little to no shelter. I was thinking this was a fallacy of suppressed correlative, but that doesn't quite seem to fit. What is the error or fallacy in this form of argument? How might one refute such an argument?

Years ago, I used to teach informal reasoning. One of the things I came to realize was that my students and I were in much the same position when it came to names of fallacies: I'd get myself to memorize them during the term, but not long after, I'd forget most of the names, just as my students presumably did. Still, I think that in this case we can come up with a name that may even be helpful. Start here: the conclusion is a complete non sequitur ; it doesn't even remotely follow from the premises. How do we get from "The poor in some countries are worse off than the poor in our country" to "The poor in our country should be immiserated until they are as wretched as the poor in those other countries"? Notice that the premise is a bald statement of fact, while the conclusion tells use what we ought to do about the fact. By and large, an "ought" doesn't simply follow from an "is", and so we have a classic "is/ought" fallacy. However, pointing this out isn't really enough. After all, in some cases...

Is there a way to confirm a premises truth? When I looked it up I found two ways suggested. The first was the idea that a premise can be common sense, which I can't compartmentalize from the idea that appeals to consensus are considered a fallacy. The second was that it can be supported by inductive evidence, which to my knowledge can only be used to support claims of likelihood, not certainty.

The answer will vary with the sort of premise. For example: we confirm the truth of a mathematical claim in a very different way than we confirm the truth of a claim about the weather. Some things can be confirmed by straightforward observation (there's a computer in front of me). Some can be confirmed by calculation (for example, that 479x368=176,272). Depending on our purposes and the degree of certainty we need, some can be confirmed simply by looking things up. (That's how I know that Ludwig Wittgenstein was born in 1889.) Some call for more extensive investigation, possibly including the methods and techniques of some scientific discipline. The list goes on. It even includes things like appeal to consensus, when the consensus is of people who have relevant expertise. I'm not a climate scientist. I believe that humans are contributing to climate change because the consensus among experts is that it's true. But the word "expert" matters there. The fast that a group of my friends happen to think that...

Is this a decent argument (i.e. logical, sound)? If God exists, God is an omniscient, omnipotent, wholly good being If God is wholly good, God would want humans to posess free will If God is wholly good, God could endow humans with free will But, if any being is omniscient or all knowing, such a being would know human choices and actions before they are chosen Under such conditions, free will would only exist as an illusion or in the mind as the human perception of having free will; true free will would not exist because God or some other power has predecided all human choices Therefore, God, if God exists, cannot be both wholly good and omniscient Therefore, God does not exist

When we look at arguments, we have two broad questions in mind. One is whether the conclusion follows from the premises, whether or not the premises are true. The other is whether the premises are actually true. So with that in mind, let's turn to the argument. It's often possible by restating premises and adding other premises that are assumed but not stated to make an argument valid even if it's not valid as stated. Your argument is more or less this, I think If God exists, then necessarily God is perfectly good, knows all, and is all-powerful, Suppose God exists. Since God is all-powerful, God can give us free will. Since God is perfectly good, God wants us to have free will. God does anything God wants to do. Therefore, we have free will. Since God knows all, God knows what we are going to do before we do it. If God knows what we're going to do before we do it, then we don't have free will. Therefore, we don't have free will. CONTRADICTION. Therefore, God doesn't exist. We could clean things...

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