In my experience, not every philosopher treats repetition as essential to a tautology. Sometimes I've seen "tautology" used to denote any logical or conceptual truth, even one that doesn't contain repetition, such as "All bachelors are unmarried." But I think most would agree that any statement that's logically true at least partly because of repetition, such as "All bachelors are bachelors," counts as a tautology. Whether the repetition is "unnecessary" requires asking, "Unnecessary for what?" If you start a statement with "All bachelors are...", there are plenty of ways to finish it that won't produce a truth, but repetition will. Yet repetition isn't necessary in order to produce a truth. Furthermore, repetition isn't sufficient for truth: "2+2=5. I repeat: 2+2=5."

Regarding whether it's true that "people [in general] make decisions primarily using emotional criteria, and only after the fact do they then use reason to justify this decision": This question is empirical, and it belongs to psychology. I wouldn't trust any philosopher as such to answer it. I'm not sure that psychology, in its present state of development, can answer it either, but philosophy as such doesn't have a hope of answering it. The claims you attribute to Marx are also empirical, and in this case best evaluated by economic historians. The claims are so sweeping that I myself would need an awful lot of evidence before I'd accept them. I'm not sure how we'd even get reliable evidence that "the foundation of all social relationships is technology, or economic relationships, or how people earn a living": the claim is not only sweeping but also ill-defined (what's meant by "foundation"?). Philosophers as such aren't equipped to answer empirical questions. But I think they...

You may find it interesting to read about the phenomenon of blindsight , which sounds roughly like what you're describing. My impression is that perhaps psychologists more than philosophers have investigated it, but there's at least one book on the topic written by someone trained in philosophy.

The intuitive answer seems to be "1 in 3," and I think that's the right answer if each infinite set of marbles has the same size (or "cardinality"). I take it you're wondering if the infinite size of the sets invalidates the intuitive answer. I don't think it does. Maybe this analogy will help. There are infinitely many even whole numbers and infinitely many even plus odd whole numbers, but there aren't twice as many of the latter as there are of the former: the cardinality of the two sets is the same. Yet the odds that a randomly chosen whole number is even are surely only 1 in 2 (rather than 1 in 1). If that reasoning is sound, then the fact that the various sets are infinite doesn't affect the probability.

By "Is it ethical to kill someone in self-defense?" I take it you mean "Is it ever morally permissible to do so?" Consider a tidy case, in which you're morally innocent and in which, for all you can reasonably tell, it's certain you'll be killed unless you kill your attacker. If it's not morally permissible for you to kill the attacker, then it must be morally obligatory for you to allow yourself to be killed: permission and obligation are two sides of the same coin. Hence, unless it's morally obligatory for you to allow yourself to be killed, it's morally permissible for you to kill your attacker. I can't see how it could be morally obligatory for you to allow yourself to be killed in that situation, so I readily conclude that you're morally permitted to kill your attacker. (I recognize that some prominent figures have taken the opposite view, apparently including Jesus in Mt. 5:39 .)

My colleagues' examples show me that my intuitions aren't thoroughly consequentialist. I think an innocent person (and maybe any person) always has a right to lethal self-defense if needed to avoid a lethal threat. An innocent person's (and maybe any person's) sacrificing his/her life is always morally supererogatory.

I think there are limits to how far the skeptical worry you describe can go. Your reference to virtual-reality devices is telling: "The thing about physical science is that it seems like it doesn't tell you anything that couldn't be simulated by a virtual reality device of some sort." Notice that it's physical science itself (computer science, neuroscience) that encourages you to say that. In broaching the idea that virtual-reality devices could fake what we take to be truths revealed by science, you make two non-skeptical assumptions: (1) Science really does claim such-and-such about reality; (2) science has it right about the power of virtual-reality devices. (Now, someone's skepticism might stem from merely imagining that reality is radically different from how it seems to him/her, but that kind of skepticism doesn't -- and shouldn't -- rely on anything scientific.) Can empirical science test a radical skeptical hypothesis? No. Of necessity, empirical scientific testing always occurs...

I confess I'm puzzled by Prof. Heck's reply. He defends the following three assumptions: (1) If you understand a proposition, then you also understand its negation. (2) It is necessary, if you are to believe a proposition, to understand it. (3) It's perfectly possible to believe a proposition and not understand its negation. I interpret those assumptions as follows: (1*) Understanding P entails understanding not-P. (2*) Believing P entails understanding P. (3*) Believing P doesn't entail understanding not-P. (1*)-(3*) imply a contradiction: Believing P does and doesn't entail understanding not-P. If so, then (1)-(3) imply everything (if I've interpreted them correctly). I also don't see how the falsity of (3) implies that we would always have to believe contradictions. If (3) is false, then believing P entails understanding not-P; I don't see how any unwelcome consequences follow from that. PLEASE NOTE : (3) above was taken from Professor Heck's original...

Your question touches on two much-discussed philosophical topics: the epistemology of (expert and non-expert) testimony and the epistemology of disagreement . You can find accessible discussions of those topics here and here . I won't opine about those topics in general except to say that the academic credentials and scholarly independence of anyone making a scientific claim are highly relevant and worth checking. Fortunately, the particular example you gave is fairly tractable: the issue "Is all animal fat harmful even if consumed in moderation?" In fact, the debate you referred to is even more tightly focused: "Is fish fat, even in moderation, harmful?" Thanks to that tight focus, you can narrow your search to sources answering that particular question. The web makes such a search easier than ever before. Start with the most recent peer-reviewed articles you find, because they're supposed to take account of and respond to earlier articles; their conclusions will be summarized...

I agree, and you'll find an ally in Hume: see this SEP entry . On the other side, philosopher Robert Kane invokes quantum indeterminism in his defense of libertarian free will; see his contributions to this volume .

You wrote, "Is it accurate to say that we 'assume' such a thing?" I don't think it's part of the concept of an assumption that all assumptions are explicit or top-of-mind when we make them. Some assumptions are merely implicit, unstated, tacit. That's why the phrase "implicit assumption" isn't a contradiction in terms. So the inductive assumptions that we make could be mostly or entirely implicit, and it may be only when such an assumption proves wrong -- for instance, when the floorboard gives out -- that we realize we were making the assumption in the first place. I think your professor is right that we do rely on inductive assumptions all the time, almost always implicitly. Philosopher David Hume (1711-1776) famously argued that we rely on inductive reasoning all the time even though we have no good reason to trust it. See also this link: http://www.askphilosophers.org/question/4574 .