Are definitions falsifiable? It seems that if I find something of category X that does not fit category X's definition, then it isn't actually of category X, and thus doesn't prove anything. But on the other hand, if that is the case, it seems no definition cannot be falsified or otherwise demonstrated to be inadequate (unless it is inherently contradictory or so).

Let's focus on the phrase "something of category X that does not fit category X's definition." One on interpretation, we can't possibly find something of that description: if it doesn't fit category X's definition, then it's not something of category X, as you say. But that interpretation assumes that I've already got a correct definition of category X, a definition that's neither too broad nor too narrow. What if my definition of 'chair' is 'item of furniture with four legs' and you show me a bean-bag chair or an IKEA Poang chair? Haven't you shown me an item of category X that doesn't fit my definition of category X? Haven't you falsified my definition of 'chair', at least as a definition of the word in ordinary use, by showing that it's too narrow? (It's also too broad, as I realize when you show me a four-legged table.)

Is similarity a fact of things in the world, or is it an observation made by sentient beings? Take two cats, for example. Is it an objective fact of the world that the two cats are similar (shape, size, biology, etc.)? Or are there, ontologically speaking, just two phenomena (or two portions of the phenomenal world) that we, as conscious beings, perceive as similar and categorize as cats?

I think it depends on what's meant by 'similarity'. If similarity is just the sharing of properties -- having in common this or that attribute -- then it would seem that any two things are similar. Even Barack Obama and the Battle of Hastings have lots of properties in common: being known to historians, being the subject of books and articles, being distinct from the number 3, being referred to by me in this sentence, and so on. (You might reply that similarity is only the sharing of intrinsic properties, but it isn't always easy to draw a line between intrinsic and extrinsic properties.) So from the perspective of the world, any two things are similar -- and maybe equally similar, since any two things share infinitely many properties. But almost all of those properties will be uninteresting to us, and that's where we come in. From among those infinitely many properties, we conscious beings focus on just a handful in accordance with our interests. If we restrict ourselves to...

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...

I was reading some questions on this site regarding vagueness and the Sorites conundrum and I'm not sure I understand the fascination with figuring out what does or doesn't qualify as a heap. Isn't the word heap useful precisely BECAUSE it doesn't have a strict quantitative requirement? We choose to use the word "heap" and not a different word (like grams, or tons, or twenty-seven, etc.) because it offers us flexibility. I'm not sure exactly why this "puzzle" has received so much attention. The fact that there hasn't been an accepted solution makes perfect sense to me because there is nothing to solve. It seems like trying to apply precision to a word intentionally designed to be imprecise. It seems to me that if we figure out the exact point at which something becomes a heap then we will no longer be able to use the word as freely. Am I misunderstanding the problem? Thanks in advance!

I think you understand at least one aspect of the problem quite well. As you say, words like 'heap' are useful only if they're vague. Indeed, their vagueness seems built into their meanings: they're essentially vague; they wouldn't be the words they are if they weren't vague. The problem is that their vagueness seems to imply the contradiction that is the sorites paradox (see the two SEP entries that I cited here ). And it's not just 'heap', a word we might not care too deeply about. Practically every concrete noun and ordinary adjective we use ('car', 'fetus', 'child', 'person', 'tall', 'rich', 'unjust', 'toxic', 'honest', 'safe', and on and on) is essentially vague and hence apparently implies a contradiction. Yet we can't help thinking that plenty of things do answer to those nouns and adjectives. Surely there are rich people and toxic chemicals, but the sorites paradox seems to show that there can't be. It's as ubiquitous as it is hard to solve.

On 2/2, I asked: What I remember from my philosophy courses is the spirited debate, lively dialogue. For me this site is too question-and-answer, like the Stanford Online Encyclopedia that is often pointed to in the responses. Is there a place on the web where I can find a more dialogue-based form of philosophy? In reply, I received 2 replies bemoaning the quality of thinking found in philosophy chat rooms. I don't believe my question implied that I wanted to chat with morons in a "philosophy chat room", but let me clarify: I graduated with a BA in philosophy from what was then ranked as the #1 liberal arts college in the US, so I'd say I can tell the difference between people who can't reason their way out of paper bags, and philosophers. But the responders seem to imply that, at their level of philosophical accomplishment, there isn't much more to be said after one respondent has answered. In my view, this implies that the quality of the questions is poor, not provoking spirited dialogue from the...

Just for the record, neither Prof. Smith nor I bemoaned the quality of thinking in philosophy chat rooms, having made it clear that neither of us had ever visited any. But we both have serious doubts about the quality of philosophical conversation to be found there, if any exist. My doubts stem from seeing non-philosophers post and comment on philosophical topics, as I said. With your own training in philosophy, you'd find those threads deeply disappointing too, I'm sure. Prof. George suggested you might find the philosophical give-and-take you're seeking on blogs run by philosophers, but naturally those focus on whatever topics the bloggers currently find interesting. If your interests happen to match theirs, and if they allow comments, you'll find something on which to comment. David Chalmers maintains a long list of philosophy blogs here . I myself like the way AskPhilosophers functions. You wrote, "[T]he responders seem to imply that, at their level of philosophical accomplishment,...

Are all non-self-contradicting ethics systems equal? Say I don't physically discipline a child because I believe it is unethical to intentionally harm another human. Do I have any reason to say that another person ought not to physically discipline their child if they believe that there is nothing unethical about harming another?

Good question. You ask if all self-consistent ethical systems are equal, by which I take it you mean "equally plausible," "equally likely to be true," or "equally defensible." The crude sample principles you gave might suggest an affirmative answer to that question, but only because they seem about equally implausible. The first principle implies that I can't justifiably harm another even to protect myself or an innocent third party from harm. The second principle implies that I can justifiably harm another for any reason, or no reason, at all. Both conflict with widely and deeply held moral intuitions that are more plausible than the principles themselves. Adherents of each principle could simply reject those intuitions, but we don't have to regard that as a successful defense of those principles. More generally we might ask, "Are all self-consistent descriptions of reality true?" Logic gives us a straightforward answer: No. Two self-consistent descriptions of reality can be inconsistent...

I read somewhere that a human being's DNA is almost the same as a rat's. (I think the percentage of similarity is 90%.) In other words, we're animals. If I saw a group of grey squirrels killing a group of brown squirrels in a park, I wouldn't judge the actions of the grey squirrels as "immoral." I would just wait for a biologist to give me some explanation. (There is a limited supply of nuts in the park; the grey squirrels have a mutation in their brain that makes them overly aggressive; etc.) So when one group of human beings commits genocide against a different group of human beings, why do we label it as "immoral" when we wouldn't do the same for squirrels (considering that humans are merely animals in the end.)

The knowledge that human beings are animals didn't, of course, await the discovery of DNA. We've known it for millennia. But your question puts enormous weight on our being merely animals: the word "merely" is being asked to do all the argumentative work. I take it you're suggesting that anything that's merely an animal can't act immorally. It's open to someone to reply that either we're not merely animals or else some mere animals can act immorally. Indeed, if there's anything we know of that can act immorally, it's an animal -- rather than a plant, bacterium, or fungus. The capacity to act immorally arises from ongoing self-awareness, rational agency, the ability to reflect on one's actions, and the like -- features possessed by some animals (including but probably not limited to our species in this vast universe) and lacked by other animals (such as squirrels). On Earth anyway, the ability to philosophize seems to be restricted to human animals. Why not, then, the ability to act...

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.' ...

What I remember from my philosophy courses is the spirited debate, lively dialogue. For me this site is too question-and-answer, like the Stanford Online Encyclopedia that is often pointed to in the responses. Is there a place on the web where I can find a more dialogue-based form of philosophy?

I second Professor Smith's reply. I haven't participated in philosophy chat rooms either, but I've commented on blogs by non-philosophers who post on philosophical topics. I've found the quality of thinking in those totally unregulated forums to be so bad it's scary. There are people in the blogosphere who are allowed to drive and vote who couldn't reason their way out of a wet paper bag. Philosophy is a discipline, one that takes hard work to acquire. Would you want to discuss medieval history, or quantum mechanics, or set theory in a dialogue format with just anyone out there? I wouldn't. Philosophy is like those other disciplines except that its problems are harder and more fundamental to our intellectual lives. Why do so many people think that being competent at it takes no training at all?

I recently asked a question about the sorites paradox, and I received the following response, which seems to me to have a logical fallacy in it. In other words, the answer below does not seem to "explain" the paradox as much as it "contains" the paradox.... Here is the reply: "Because the paradox itself results from commitments of common sense: (a) some number of grains is clearly too few to make a heap (maybe 15, as you say); (b) some number of grains is clearly enough to make a heap (maybe 15,000); and yet (c) one grain never makes the difference between any two different statuses (heap vs. non-heap, definitely a heap vs. not definitely a heap, etc.). Given commonsense logic, (a)-(c) can't all be true, but which one should we reject? Most philosophers who try to solve the paradox attack (c), but I certainly haven't seen a refutation of (c) that I'd call 'commonsense.'" It seems that point (c) above presupposes that either we have 100% heap or 0% heap; however if we can have a number of grains such...

I supplied the response you found unsatisfying, so thanks for not pretending you were satisfied by it! You're right that my response did assume that there's only a "yes" or "no" answer to such questions as "Can N grains (for some particular N) make a heap?", "Can N grains definitely make a heap?", and so on. I also claimed that my assumption was an element of common sense. As I understand it, your counter-proposal is that N grains can be enough to make, for instance, "an 85% heap" (or maybe "85% of a heap") but not "a 100% heap" (or maybe "100% of a heap"). But what's an 85% heap? What's 85% of a heap, except a smaller heap? More plausibly, maybe you're proposing that the statement "N grains can make a heap" is only 85% true rather than 100% true. Proposals of this sort are well-known in the literature on the sorites paradox, usually under the heading of "many-valued logics" (see section 3.4 of the SEP article "Sorites Paradox" that I linked to in my previous reply). These many...

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