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Logic

Are slippery slope arguments ever non-fallacious? Or, put another way, should we ever find slippery slope arguments persuasive?

Slippery slope arguments generally have the following form. (1)If we allow X, then we will have no principled ground for resisting Y(once you step onto this slope at X, you’ll fall all the way to Y). (2) Y is obviously a bad thing. (3) Therefore, we shouldn’t allow X. So, for example, (1) If we allow physician-assisted suicide, then we’ll have no principled grounds for resisting involuntary euthanasia. (2) Involuntary euthanasia is obviously immoral. (3) Therefore, we ought not to allow physician-assisted suicide. Asyou can see from my example, whether a given slippery-slope argument iscompelling will depend on the plausibility of the first premise in thisargument form.
Identity
Logic

How do formal logicians respond to Marxist/Leninist/Dialectical logic claims? For example, in "An Introduction to the Logic of Marxism", George Novack explains that the law of identity of formal logic, that "A is equal to A", is always falsified when we try to apply it to reality. Here is a quote from the book, in which he quotes from "In Defense of Marxism" (it is long, I apologize): "... a pound of sugar is equal to itself. Neither is this true -- all bodies change uninterruptedly in size, weight, color, etc. They are never equal to themselves. A sophist will respond that a pound of sugar is equal to itself at 'any given moment.' "Aside from the extremely dubious practical value of this 'axiom,' it does not withstand theoretical criticism either. How should we really conceive the word 'moment'? If it is an infinitesimal interval of time, then a pound of sugar is subjected during the course of that 'moment' to inevitable changes. Or is the 'moment' a purely mathematical abstraction, that is, a...

According to a standard conception of identity, if A is identical to B , then A and B haveall of their properties in common. This principle is commonly known asLeibniz’s law, after the philosopher Gottfried Wilhelm Leibniz, a 17thcentury German philosopher, who articulated this implication of ourconcept of identity. This principle is also referred to as "theprinciple of the indiscernibility of identicals". This law or principlemight seem to imply that if a particular object (say a particularquantity of sugar) changes over time, then it’s not the same thing–after all, the properties of the object at one time are different fromthe properties of that object at another time. However, this reasoningrests on a confusion. Leibniz’s law does not imply that if A at T1 has properties f , g , and h , then A at T2 must have these same properties. Instead, it implies that, if it is true of A that at T1 it has properties f , g , and h , then at T2 it is true of A that...
Knowledge
Logic

I once took a graduate course in education in which I was the only non-teacher. One day, I disagreed with something said by another student, and her response has always baffled me. She said: "Who are you? You can't question me until you've walked in my shoes." In other words, she felt that I was unqualified to question her, to cast doubt on anything she said. Who was I to say? Well of course her response was nonsense but how so? As a matter of logic or illogic, was her remark an example of an appeal to authority? She certainly felt that she was an authority.

I have such a visceral reaction to your fellow student’s comment. I just want to slap her on your behalf, which of course I’d never do, but I’d want to! But then I wonder what your comment was. Maybe she was just verbally slapping you, and while verbal slapping is no better than physical slapping, it is just as understandable. But let’s assume that what you said was perfectly reasonable. As a hypothetical example, let’s assume that you were respectfully questioning her view about how to handle disciplinary issues that arise in the classroom. And let’s take her claim not as a verbal slapping, but as a serious claim about the conditions under which you count as having the epistemic authority to question her. She claims that you can’t question her unless you walk in her shoes. Does this mean that you can’t ask her a question? Surely, she can’t mean this. So I suppose that she means that you are not epistemically permitted to doubt the truth of her judgment. And what does she mean by the...