Why is C.I. Lewis' strict implication not taken seriously in this day and age? Clarence Irving Lewis was known for criticizing material implication and for instead proposing strict implication. Why is he, his criticisms, and his proposed strict implication not taken seriously today? Many contemporary logic, philosophy, and mathematical texts refer to material implication rather than strict implication.

I'd say that C. I. Lewis's strict implication is very much alive in contemporary philosophy, although often called by different names, such as "logical entailment" or "logical implication." Philosophers frequently claim (or deny) that some proposition "entails" another, by which they very often seem to mean "strictly implies." Material implication, unlike strict implication, is a truth-functional relation between propositions: given only the classical truth-values of two propositions, you can tell which one materially implies the other (material implication will run in at least one direction between them, if not both). By contrast, strict implication isn't truth-functional: it requires asking about the truth-values that propositions take in worlds other than the actual world, which invites philosophical controversy. As a result, strict implication is a less clear-cut relation than material implication. So despite its unintuitive features (which, as you say, Lewis criticized), material...

Can tautology be defined as "unnecessary repetition of information"? In other words, does tautology have the same sense as repetition? Thanks.

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."

I've heard it asserted several times in quite different contexts that "people make decisions primarily using emotional criteria, and only after the fact do they then use reason to justify this decision." I'm curious both to hear your response(s) in general, and perhaps also in a more specific context. If I understand Karl Marx' economic theory correctly, he asserts that the foundation of all social relationships is technology, or economic relationships, or how people earn a living. Social, political, religious, and governmental structures then develop as a justification of the fundamental underlying economic relationships. I'm curious on philosophical responses to this assertion, because it seems to me that it is the basis for the crucial argument that then follows. He then asserts that, because technology is constantly evolving, while bureaucratic structures are static, that a "dissonance" develops over time, which must eventually result in a re-balancing. so that the other structures are then in...

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...

Is it considered possible to be consciously aware of an object or thought without experiencing feelings, or is "feelings" just another word for conscious awareness?. If this question can't be dismissed, which philosophers have explored it?

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.

Suppose that you had two bags each with an infinite number of blue marbles. Suppose you also had another bag of infinity red marbles. If you mixed those three bags what are your odds of getting a red marble? Obviously this isn't a realistic experiment but is it 1 in 3 or 50%?

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.

Is it ethical to kill someone in self-defense? My instinct was yes at first, but upon further reflection, in a situation where it's "you or them", I can't seem to think of a reason to kill someone in self-defense, other than the fact that you simply want to live. After all, you're still taking a human life. (Also if you could explain why it is or isn't ethical would help me out a lot thanks!)

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.

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 .)

The thing about physical science is that it seems likes it doesn't tell you anything that couldn't be simulated by a virtual reality device of some sort. Am I wrong? Can science test that hypothesis in a reasonable way? It seems like the only real and accessible metaphysical qualities are things like color. Color is real whether we are looking at a virtual reality simulation or something else. "Has science allowed us to go deeper than that to an actual world behind manifestations such as color?

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...

Is "understanding" a proposition necessary, but not sufficient, for "believing" that same proposition? Further, where could one find arguments (discussion) for and/or against either position?

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...

I often read that we must judge arguments or claims based on their own merits, rather than on the quality of the person presenting them. This is fine in realms such as logic or everyday life, where we can all have access to the relevant information, but how does this play out in complex domains, such as science? For instance, suppose I am reading two books on the health effects of different nutrients, such as animal fat. One author claims all animal fat is harmful, the other claims that some animal fats, such as fish fat, is fine in moderation. Both cite studies supporting their views, but one author is a spokesperson for PETA and the other is a senior researcher at a well-known university. As somebody who doesn't have access to biology laboratories to conduct experiments, and who perhaps doesn't have the time to read every source cited, critique every study made and read every attack made on both author's views, what is the best thing for me to do? Should I simply decide not to believe anything at...

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...

Pages