Edwina, List: Validity is not a matter of fact, it is a matter of form. A perfectly *valid *deductive argument can produce a false conclusion, and therefore be *unsound*, simply because at least one of its premisses is false. A perfectly valid retroductive argument can also produce a false conclusion, even if--as in this case--both premisses are true, simply because its proper form does not *guarantee *a true conclusion from true premisses. Of course, Peirce was quite adamant that the conclusion of a valid retroductive argument is nevertheless a *logical inference*, just of a different type than that associated with deductive reasoning.
Regards, Jon On Thu, Oct 5, 2017 at 5:14 PM, Edwina Taborsky <[email protected]> wrote: > Yes, you are nitpicking. I agree with your comments about terminology but > they divert from the issue. > > And no- I disagree with your 'retroductively valid' point, for the > empirical fact - i.e. 'it is true that it did NOT rain' - precludes any > validity. We aren't talking about plausibility but about facts. > > Edwina > > On Thu 05/10/17 5:36 PM , Jon Alan Schmidt [email protected] sent: > > Edwina, List: > > ET: 2] If it rains, my car will get wet. My car is wet: Therefore, it > rained. > > ET: The premises are valid. But the conclusion is invalid - I left the > sprinkler on. > > > Admittedly nitpicking here, but premisses are not "valid," they are > either true or false; only arguments are valid or invalid. Also, in this > case the argument is deductively invalid, but retroductively valid--i.e., > the hypothesis that it rained is a plausible explanation of the > surprising fact that my car is wet, given my knowledge of the rule that a > wet car would be an outcome of it raining. > > Regards, > > Jon Alan Schmidt - Olathe, Kansas, USA > Professional Engineer, Amateur Philosopher, Lutheran Layman > www.LinkedIn.com/in/JonAlanSchmidt - twitter.com/JonAlanSchmidt > > On Thu, Oct 5, 2017 at 2:24 PM, Edwina Taborsky <[email protected]> > wrote: > >> Helmut, list - but, can't an inference be illogical in its format? >> >> For example: >> >> 1] All cats are animals/ All dogs are animals: Therefore, all cats are >> dogs. >> >> The premises of the above syllogism are valid; but, the reasoning or >> conclusion is invalid. [Undistributed middle]. >> >> 2] If it rains, my car will get wet. My car is wet: Therefore, it rained. >> >> The premises are valid. But the conclusion is invalid - I left the >> sprinkler on. >> >> Your outline of the three methods of reasoning is a different topic than >> a discussion on ''inference' or 'conclusions'. >> >> Edwina >> >
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