My apologies, I need to make a correction to the last paragraph of my previous message; see below for the revised version. *Modus ponens* and "affirming the consequent" pertain only to propositional logic, not predicate logic.
Jon S. On Tue, Apr 26, 2016 at 1:52 PM, Jon Alan Schmidt <[email protected]> wrote: > Jerry R., List: > > *Modus ponens* is a deductively valid form of argument in propositional > logic. By contrast, as Edwina just pointed out, the form of (abductive) > argument in CP 5.189 is deductively INvalid; it commits the fallacy known > as "affirming the consequent." > > Valid *modus ponens* = If p then q / p / Therefore q. > Invalid affirming the consequent = If p then q / q / Therefore p. > > Surprise is indeed the motivation for an abductive inference, and > suspicion is indeed its result--but these are two *different* emotions; > in fact, the latter is what *dissolves* the former. "The irritation of > doubt [prompted by observation of a surprising fact] causes a struggle to > attain a state of belief [suspicion that a particular hypothesis is true]." > (CP 5.374, EP 2.114) > > I hate to belabor this, but I feel the need to point out one more time > that the syllogism described by Peirce in "A Neglected Argument" (EP 2.441) > is clearly NOT the abductive formulation in CP 5.189. He states that the > two premises of the syllogism that he has in mind are "the circumstances of > [the surprising fact's] occurrence together with the truth of the credible > conjecture," and that what follows from them "as necessarily consequent" > (i.e., deductively) is "the surprising fact" itself. > > Premiss: circumstances of occurrence (M is P). > Premiss: credible conjecture or hypothesis (A = S is M). > Conclusion: surprising fact (C = S is P). > > This is deductively valid, rather than the abductive form of CP 5.189 that > is deductively invalid. For the bean example, S = "these beans," M = > "beans from this bag," and P = "white." > > Regards, > > Jon Alan Schmidt - Olathe, Kansas, USA > Professional Engineer, Amateur Philosopher, Lutheran Layman > www.LinkedIn.com/in/JonAlanSchmidt - twitter.com/JonAlanSchmidt > > On Tue, Apr 26, 2016 at 1:05 PM, Jerry Rhee <[email protected]> wrote: > >> Ben, >> >> >> >> Thanks for that. Your explanation works for me but it also leaves me a >> little unsettled. >> >> >> >> First of all, is modus ponens simply indicated by switching the order of >> the three lines? >> >> >> That is, >> >> “If *p* then *q*. = “But if A were true, C would be a matter of course” >> >> * p*. = “The surprising fact C is observed” >> >> Ergo, *q*. = “Hence there is reason to suspect that A is true” >> >> >> >> The difference I see here is that p = A in the first line but p = C in >> line 2. >> >> Similarly, q = C in the first line but q = A in line 3. So, they switch. >> In like manner, the attitude of the inquirer switches from surprise to >> suspect. >> >> >> >> Moreover, Randy Goebel gives the formulation, >> >> *From P, and Q => P, infer Q*, which isn’t exactly the same as modus >> ponens. >> >> >> >> Additionally, the motivation for the inference itself is a HUGE matter, >> one that requires bringing attention to specific things (e.g., *black* >> beans and not just beans because black beans to me is not surprising but to >> you, it is) because if you don’t have the motivation, where is the inquiry >> (c.f., fingers example in *Republic*)? >> >> >> >> As you say, “The emotion of surprise mentioned in the abductive schema is >> affected, and in particular, reduced or eliminated, by the abductive >> inference itself.” But isn’t that what is being stated in the NA? “*The >> inquiry begins with pondering these phenomena in all their aspects, in the >> search of some point of view whence the wonder shall be resolved*.” >> >> >> >> If Peirce is intending to treat “C & A without B because he is treating >> abduction as a transformation of *modus ponens” *only, he could have >> simply stated it as B & A instead of C & A since A and B are necessarily in >> sequence. So, why A to C by leaving out B? That is a surprising fact >> that I observed. >> >> >> >> This goes to the overall hypothesis that the NA is simply a demonstration >> of the abductive method. The Additament, if I recall correctly, gives a >> fuller account of deduction and induction. >> >> >> >> Thanks for your work on this and for providing such direct responses to >> my questions throughout. I truly appreciate it. >> >> >> Admittedly, I think I err in saying that CP 5.189 is a syllogism; that I >> am taking too many liberties in saying that they are the same and not >> respecting the history and rules of logic. There is also the matter that I >> do not know that history and rules well enough to even speak on it. Yet, >> this is the manner in which I pursue the inquiry. The two may not be >> identical but my hypothesis is that the essence of syllogism is maintained >> in CP 5.189 to be able to call it syllogism and to even claim a "technical" >> correctness because: >> >> >> “At length a conjecture arises that furnishes a possible *Explanation, >> by which I mean a syllogism* exhibiting the surprising fact as >> necessarily consequent upon the circumstances of its occurrence together >> with the truth of the credible conjecture, as premisses. *On account of >> this Explanation, the inquirer is led to regard his conjecture, or >> hypothesis, with favour*.” >> >> >> That is, by calling CP 5.189 a syllogism, it harmonizes Peirce's ideas in >> unity. >> >> >> >> With best wishes, >> Jerry R >> > >
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