It is not only overtly probabilistic illatives like ‘makes it certain that’ but also apparently non-probabilistic ones like ‘therefore’ that have probabilistic import. Illatives like ‘therefore’ convey the meaning that the premise confers on the conclusion a probability not only greater than 0 but also greater than 1/2. But because they do not say whether that probability is equal to or less than 1, these illatives are appropriately called ‘neutral’.

In this paper I examine five distinctions between deductive and inductive arguments, concluding that the best of the five defines a deductive argument as one in which conclusive favorable relevance to its conclusion is attributed to its premises, and an inductive argument as any argument that is not deductive. This distinction, unlike its rivals, is both exclusive and exhaustive; permits both good and bad arguments of each kind; and is both useful and needed in evaluating at least some arguments.

The thesis of this paper is that an argument's possessing the form of affirming the consequent does not suffice to make its premises at all favorably relevant to its conclusion. In support of this thesis I assume two premises and argue for a third. My two assumptions are these: (1) that an argument's possessing the form of affirming the consequent does not suffice to make its conclusion certain relative to its premises (this is widely, if not universally, acknowledged by writers (...) on logic), and (2) premises are favorably relevant to a conclusion only if it is certain or probable relative to them (I argued for this in an earlier paper). The premise I argue for in this paper is that an argument's possessing the form of affirming the consequent does not suffice to make its conclusion probable relative to its premises. To establish this third premise, I first refute a defense of the contrary position (namely, that an argument's possessing the form of affirming the consequent suffices to make its conclusion probable relative to its premises), then offer counterexamples to that position, and finally demonstrate the failure of several attempts to save it. (shrink)

I first support Alec Fisher's thesis that premises and conclusions in arguments can be unasserted first by arguing in its favor that only it preserves our intuition that it is at least possible that two arguments share the same premises and the same conclusion although not everything that is asserted in the one is also asserted in the other and second by answering two objections that might be raised against it. I then draw from Professor Fisher's thesis the consequence that (...) in suppositional arguments the falsity (or unacceptability) of a supposition does not tell unfavorably in the evaluation of the argument, because the falsity (or unacceptability) of a (nonredundant) premise counts against an argument if and only if that premise is asserted. Finally, I observe that, despite the fact that they are neither expressed nor even alluded to, implicit assumptions in arguments are always asserted, unless the conclusion, but none of the explicit premisses, is unasserted. Hence, apart from an exceptional case of the kind just mentioned, the falsity (or unacceptability) of implicit assumptions always counts against an argument. (shrink)

I reply to three criticisms of my "Propositional Relevance" offered by Derek Allen, First, Professor Allen points out an inconsistency between my theory of relevance and my reply to an objection, I admit the error but add that it is remediable. Second, he argues that my theory of relevance is counterintuitive. I argue that it is not. And finally, he says that where I use phrases like 'p makes q certain,' I should instead use phrases like 'p, if true, makes (...) q certain.' I argue against this. (shrink)

According to the Asymmetry Thesis, whereas there are many kinds of argument-forms that make at least some of their instances valid, there is none that makes any of its instances invalid. To refute this thesis, a counterexample has been produced in the form of an argument-form whose premise-form's instances are all logically true and whose conclusion form's instances are all logically false. The purpose of this paper is to show that there are many more kinds of argument-forms that make some (...) of their instances invalid and that, hence, are counterexamples refuting the Asymmetry Thesis. (shrink)