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Do we have a duty to strive towards a life without contradiction? Can a person,

Do we have a duty to strive towards a life without contradiction? Can a person, for example, both eat meat and hold the belief that animals should not be willfully killed for private gain?

Well, one CAN do that, since I myself in fact do (and many, many others) .... But of course what you're asking is more like "is it morally permissible to violate one's own principles?", or something like that ... Assuming that one's principles are correct (i.e. that you are right to believe that animals shouldn't be willfully killed etc.), then it seems clear that the answer must be no, because it's not morally permissible to do that which is morally impermissible! But that seems so clear that I wonder if that really is, ultimately, your question. Weakness of will is a well-known (and much discussed phenomenon), and a paradigm case of weakness of will is precisely that where you cannot bring yourself to do that which is right (and so when I succumb, and eat meat, I condemn myself for not being able to live up to my own standards). But you seem to be getting at a much deeper question, which the weakness of will case is merely a simple case of: is there a moral obligation to avoid contradictions, to seek truth, etc. The possible contradictions in question, here, aren't between your beliefs and your actions (which aren't strictly contradictions, actually, but close enough), but between beliefs -- and here I don't have any clear intuitions about what to say. If we are morally obliged to do the right thing then, presumably, we have some moral obligation to form the correct moral beliefs; but, aside from morality/behavior, do we have any moral obligation to seek truth and avoid error? If that is, ultimately, what you're asking, then it strikes me as a really deep and hard question about which I have nothing substantial to say .... (Would be interesting to explore this question both within, and without, religious frameworks ....)


When someone says "That seems(or does not seem) logical" it is not always easy

When someone says "That seems(or does not seem) logical" it is not always easy to know how they define "logical". Is it meaningful at all? I guess the question relates to the use of something that seems to be a looser term than e.g. "deductively valid" or the like, which refers to a particular system of inference and specific rules for determining truth or falsehood of propositions. Do you have any idea as to what the term commonly refers to?

I don't really, but it is one of my biggest pet peeves, from the perspective of one grading students' philosophy papers! ... My guess would be that on many such occasions, the person means something like "valid" -- where "valid" does NOT mean the technical deductive notion but something closer to "true"! (They will often say, "P is not logical," clearly meaning that P is false ...) Occasionally people use it with a defeater: "P seems logical, and yet here's why it's false ..." On such uses they seem to mean "apparently true, even if not really true." Rarely do they use it with anything very close to its basic sense, if not quite "deductively valid" then at least bearing some relationship to arguments and conclusions (where to say "P is logical" would be to say "P is based on some form of argument") ....


It has long seemed to me that philosophers do not seem concerned with illusion,

It has long seemed to me that philosophers do not seem concerned with illusion, i.e., the appearance of reasoning that SEEMS valid but is at least questionable if not illusory. The Greek philosophers that I read in school seemed particularly questionable. My impression was that much of their argumentation was illusory, i.e., based on claims that are unidentified assumptions. An example of illusion is the argument that since everything has a cause, there must be a FIRST cause. This SOUNDS sound but of course is not. Causality is not simple and is not a matter of logic. Causality has to do with nature and we know very little about nature. For all we know the universe has been going on forever, i.e., had no beginning. Moreover, if EVERYTHING has a cause, then there cannot be a FIRST cause which is exempt from having a cause. Are there philosophers who are concerned with this problem of illusory or unfounded philosophical reasoning? I would love to read their ideas. Please note that I'm not calling...

You wrote, "It has long seemed to me that philosophers do not seem concerned with...reasoning that SEEMS valid but is at least questionable if not illusory." I must say I find that surprising, since philosophers devote a great deal of their time (and some of them virtually all of their time) to exposing hidden assumptions, faulty inferences, equivocations, etc., in the arguments of other philosophers. Indeed, much of the progress in philosophy comes from exactly this activity. The First-Cause Argument that you mentioned is a great example. Its many versions have been subjected to detailed and powerful philosophical criticism for centuries. You'll find a helpful summary of that criticism here. Among the important objections is one that you raised: Who says the universe had a beginning? There are quasi-scientific arguments that it did in fact have a beginning (based on Big Bang cosmology) and philosophical arguments that it must have had a beginning (based on the alleged impossibility of an actually infinite sequence of past events). I've never found either of those arguments persuasive. But I leave it to you to read and judge. More generally: the Western philosophical tradition is absolutely chock-full of attempts to show that seemingly sound arguments are in fact illusory.

As a student of law with a vivid interest in logic (in a broad sense), I find

As a student of law with a vivid interest in logic (in a broad sense), I find myself intrigued by the possibility of combining these two subjects. From what I so far have found, the implementation of the latter field of thought to legal discipline is mostly only done with regard to informal logic, with fairly simple overviews of the rules of inference etc.; the scope is mostly one aimed to serve the practical law-man in, say, procedural contexts. The ones that serve the academic community, seem not to be quite technical. Yet, the legal system seems highly infested with what logic is concerned. The relation between propositions of facts and norms, the norms being constructed with the help of sentential connectives, say, material conditionals or bi-conditionals to name just a few. Yet other phenomena could be named: judgments and other propositional attitudes, the normative "it is the case that", whose descriptive accuracy depends on what legal institution one is in(e.g. penal-law demands higher...

I would hope that my colleagues might be able to answer your question better than I can with respect to the law and logic in philosophy, but I can try to give you some pointers to the literature on the law and logic in artificial intelligence.

The first pointer is not so far removed from philosophy. My former colleague in the School of Law at the University at Buffalo, L. Thorne McCarty, applied deontic logic to legal issues, often citing the work of the philosopher Hector-Neri Castañeda. See, e.g., McCarty, L. Thorne (1983), "Permissions and Obligations", Proceedings of the 8th International Joint Conference on Artificial Intelligence (IJCAI-83; Karlsruhe, W. Germany) (Los Altos, CA: Morgan Kaufmann): 287-294.

There is also a journal, Artificial Intelligence and Law, which occasionally has papers that you might find relevant.

What are some of the most common mistakes of reasoning or logic that you have

What are some of the most common mistakes of reasoning or logic that you have experienced being made by non-philosophers? What are some aspects of reasoning schools should particularly focus on?

In my experience, maybe the most common mistake in reasoning committed by non-philosophers (and certainly among the most exasperating) is the one that philosopher Paul Boghossian complains about here: "Pinning a precise philosophical position on someone, especially a non-philosopher, is always tricky, because people tend to give non-equivalent formulations of what they take to be the same view" (my italics). Boghossian's complaint in this case stems from the "defense" of moral relativism offered by the literary critic Stanley Fish: "Fish, for example, after saying that his view is that 'there can be no independent standards for determining which of many rival interpretations of an event is the true one,' which sounds appropriately relativistic, ends up claiming that all he means to defend is 'the practice of putting yourself in your adversary's shoes, not in order to wear them as your own but in order to have some understanding (far short of approval) of why someone else might want to wear them.' The latter, though, is just the recommendation of empathetic understanding and is, of course, both good counsel and perfectly consistent with the endorsement of moral absolutes" ("The Maze of Moral Relativism," NYT, 24 July 2011).

It's an exasperating move in a debate because it means that one side keeps moving the goalposts without admitting (or maybe even recognizing) that they're doing it. I think only systematic study of logic can help people reliably avoid fallacies of that kind.

Judging from the students who arrive in my first-year courses, I think that any elementary or secondary schools that focus at all on reasoning -- by teaching logic as such -- are already doing better than the average school and spending their time more wisely than most.

I seem to remember the "heap paradox" being a very old one (given a heap and

I seem to remember the "heap paradox" being a very old one (given a heap and repeatedly removing a single grain of sand, when does it stop being a heap?). Yet I don't ever recall hearing a solution to it. No doubt there are different views of things, but is there at least a generally accepted solution to this paradox?

You asked, "Is there at least a generally accepted solution to this paradox?" Not by a long shot! The paradox of the heap (and its cousins that use other vague concepts) is in my opinion one of the greatest unsolved intellectual problems. It has generated a huge philosophical literature, and it's very much a topic of current philosophical debate, but I have yet to see a proposed solution that even comes close to being satisfactory. For starters, you might take a look at these entries from the Stanford Encyclopedia of Philosophy:

SEP, "Sorites Paradox"
SEP, "Vagueness"

Best wishes as you work your way through this daunting -- but inescapable -- problem! I think you'll find it repays your careful thought even if you don't end up much closer to a satisfying solution.

Is an emotional reaction to a fact/situation a logical conclusion that follows

Is an emotional reaction to a fact/situation a logical conclusion that follows from observed premises? Is it logical, for instance, to mourn the death of a loved one, or is mourning a phenomenon independent of logical analysis of a situation?

Great question that gets to the heart of a current debate! If you have a very narrow concept of logic (in which logic only refers to the laws of identity, non-contradiction, and the law of excluded middle) and if your notion of observation is again narrow perhaps only allowing in empirical data then perhaps it is neither logical nor illogical to mourn the death of someone. BUT, you may have a broader concept of observation. For example, in your question you refer to "a loved one." Can one observe the fact that a person is worthy of love or should be loved? I personally think one can. In that case, it would be quite logical (you would be acting with consistency) for you to act in a way that is appropriate when one's beloved one dies. On this expanded front, imagine you truly love Skippy and desire her or his happiness; that is, you believe it would be good for Skippy to be happy and bad if Skippy were to die before fulfilling the desires of his or her heart. Then, surely, it appears you should mourn Skippy's death. Matters may turn out otherwise, however, if you deeply restrict concepts like love, logic, and observation. I suggest the more open approach is the better one in that it captures more fully the way in which our experience is saturated with values that call for our response. You might check out Parfit's extraordinary two volume work On What Matters for a look at the issues and why there is some dispute today among philosophers on the fact/value distinction.

Recently I tried to explain to a friend what interested me about Hume's 'problem

Recently I tried to explain to a friend what interested me about Hume's 'problem of induction.' I told him how if we want to give an argument for the superiority of inductive reasoning (concluding x's are always P, based on observed instances of x's that are P) over, say, anti-inductive reasoning (concluding x's are not always P, based on observed instances of x's that are P) then we would have to give either an inductive argument or else a deductive argument. We cannot give such a deductive argument, I told him, and to give an inductive argument like 'inductive reasoning has led to good results in every observed instance' would be circular. He replied with the question 'why is there no problem of deduction?' He asked why he couldn't give a similar argument that any defense of deductive reasoning (concluding C based on premises that logically entail C) over, say, anti-deductive reasoning (concluding not C based on premises that logically entail C) needs to be either deductive or inductive. A deductive...

Rather than offer a response to this excellent question, let me just refer you to a paper whcih essentially raises and discusses the very same problem: Susan Haack's "A Justification of Deduction," from the journal Mind in 1976 (try vol 85, n. 337 I believe). Also, Lewis Carroll (as in "Alice in Wonderland" has a similar, more fun version of it -- "What the Tortoise said to Achilles" -- also in Mind, in 1895 or so ... Check them out!


Hello, I would like to ask a kind of multiple angled question I have noticed a "lack of" while studying logic. Is "the process of elimination" a sound "Rule of Inference"? (Perhaps, we've all used this "process of elimination" in taking a multiple choice test.) I have read two books on Logic: one by Irving M.Copi & Carl Cohen as well as The Logic Book by Merrie Bergmann, James Moor, Jack Nelson. I have not seen a single logic text nor a logic website where "the process of elimination" appears as a inference rule. Why is this not included as a rule? Is it not considered Deductive? Does it go by another name? What is the deal? Thank you for considering this question in advance.

It goes by another name, sometimes "argument by cases" or "argument by dilemma" or "the disjunctive syllogism". The basic rule is:

A ∨ B
∴ B

Obviously, this can be extended to any number of disjuncts, e,g.:

A ∨ B ∨ C ∨ D
~A ∧ ~B ∧ ~C
∴ D

So the disjuncts represent the possibilities you have before you, and the negations represent your ruling out all but one of them.

There are quantificational versions as well, e.g.:

∀x(Fx → x = a ∨ x = b ∨ x = c)
~Fa ∧ ~Fb
∴ Fc

This would normally be derived from one of the propositional versions.

Let's say I have a machine with a button and a light bulb where the bulb lights

Let's say I have a machine with a button and a light bulb where the bulb lights up if and only if I press the button. I don't know anything about it's inner workings (gears, computers, God), I only know the "if and only if" connection between button and light. Can I say that by pressing the button I cause the bulb to light up? (I would say yes). It seems to me that for the causal connection it doesn't matter that I don't know the exact inner workings, or that I don't desire the effect (maybe I press the button just because I enjoy pressing it, or because there is strong social pressure to press it, ...), and that I consider it very unfortunate that the bulb lights up wasting electric energy. Let's now change the terms: instead of "pressing the button" we insert "having a kid" and instead of "the bulb lights up" we have "the kid dies" (maybe when adult). I think the "if and only if" relationship still holds, and so does the causal connection. It would seem to me that parents are causally connected to...

Great set of thoughts, here. But maybe one quick mode of response is to remark that much depends on just what you take the word "cause" to mean. You could take it to mean something like this: "x causes y" = "y if and only if x", as you've suggested. Then, granting that both cases above are cases fulfilling the "if and only if", sure, giving birth would count as a cause of the later death. But now two things. (1) Why should "cause" mean precisely that? Wouldn't it be enough if the x reliably yielded the y, even if things other than x could yield the y too? (i.e. couldn't you drop the 'only if' part, so 'x causes y' would mean 'if x, then, y', even if it might also be true (say) that 'if z, then y'?) Going this route would preserve your intuition that both cases above are cases of causation, but focus on whether your particular definition is the best one. (2) Perhaps more importantly, though, one might examine the 'pragmatics' of causation -- how people actually use the word, different from how very precise philosophers or scientists might define it. So, for example, we often restrict the word 'cause' not just to every factor which may be necessary or sufficient or both for an effect, but to the most salient factors, the most explanatorily relevant ones, the most proximate ones, etc. So, you strike a match and it lights; strictly speaking many things are at least necessary for that (the presence of oxygen, the existence of the match, the laws of physics, etc.) but we often say 'the striking caused the lighting', even though all those other factors were necessary. Indeed the striking was neither necessary nor sufficient for the lighting -- the match could have been lit other ways, and striking on its own (without oxygen etc) wouldn't light. So our ordinary use of 'cause' is far looser than some technical philosophical definition. So the question for you is: how, ultimately, are you going to use the word 'cause', and are you justified in choosing that use in light of competing uses?

hope that's useful ...