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 *modus ponens*, rather than the abductive form of
CP 5.189 that is deductively invalid ("affirming the consequent"). 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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