Edwina, List: ET: All dogs are animals/All cats are animals. BOTH these premises are true. Can I logically then state that All dogs are cats?
No, and why not? Because the conclusion *does not* follow necessarily from the premisses; the *form *of the argumentation is *invalid*. The same is true of the other examples below. Now consider a different one--all dogs are animals, and Rover is a dog; can I logically then state that Rover is an animal? Yes, because the conclusion *does *follow necessarily from the premisses; the *form *of the argumentation is *valid*. My Semeiotic Argumentation has *exactly the same form *as the second case, not the first case or any of the others below; therefore, it is *valid*, such that the conclusion *does *follow necessarily from the premisses. - Every Sign is determined by an Object other than itself = all dogs are animals, and - The entire Universe is a Sign = Rover is a dog; therefore, - The entire Universe is determined by an Object other than itself = Rover is an animal. So I suppose that I should have said explicitly what I took to be obviously implied--for any *valid *deductive argumentation, the conclusion is only as strong as the premisses. If one premiss is false, then the conclusion is false, or at least unwarranted on the basis of that premiss; e.g., if the entire Universe is *not *a Sign, or if Rover is *not *a dog. However, anyone who affirms all of the premisses is rationally required to affirm the conclusion, as well. Regards, Jon Alan Schmidt - Olathe, Kansas, USA Professional Engineer, Amateur Philosopher, Lutheran Layman www.LinkedIn.com/in/JonAlanSchmidt - twitter.com/JonAlanSchmidt On Mon, May 20, 2019 at 8:04 AM Edwina Taborsky <tabor...@primus.ca> wrote: > JAS, list > > The problem I have with this claim is that it is invalid. > > JAS: As with any logical or mathematical "proof"--i.e., any deductive > argumentation--the > conclusion is only as strong as the premisses. If one premiss is false, > then the conclusion is false, or at least unwarranted on the basis of > that premiss; but anyone who affirms all of the premisses is rationally > required to affirm the conclusion, as well." > > For example, > > All dogs are animals/All cats are animals. BOTH these premises are true. > Can I logically then state that All dogs are cats? > > How about: > > The robber wears size 12 boots/ You wear size 12 boots. Both premises are > true. So, YOU are the bank robber. > > All plumbers repair sinks/ Henry repaired this sink. [both premises are > true]. So- can we say that Henry is a plumber? > > All men are rational animals/No woman is a man. [All true]. Therefore no > woman is a rational animal. > > And so on... >
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