A implies B is false iff A is true and B is false. --- Frank C. Wimberly 140 Calle Ojo Feliz, Santa Fe, NM 87505
505 670-9918 Santa Fe, NM On Tue, Dec 27, 2022, 10:15 AM David Eric Smith <[email protected]> wrote: > Are you sure Frank? > > The sentence from gtp that I highlight said: > > "⊃" is the logical symbol for "implies." It is used to form conditional >> statements in which the formula on the right is true only if the formula on >> the left is true. > > > As I understand “implies” (or just the conditional if A then B), it means > that the formula on the right is true _if_ the formula on the left is > true. Not “only if” as gtp is quoted to say above. Correct would be “the > formula on the right is _false_ _only if_ the formula on the left is > _false_. Conditional doesn’t say anything about whether B is true or false > if A is not true. > > Eric > > > > On Dec 27, 2022, at 11:46 AM, Frank Wimberly <[email protected]> wrote: > > I've taken courses in formal logic at multiple levels. All that notation > is familiar and the explanation seems correct if vacuous. > > --- > Frank C. Wimberly > 140 Calle Ojo Feliz, > Santa Fe, NM 87505 > > 505 670-9918 > Santa Fe, NM > > On Tue, Dec 27, 2022, 3:19 AM David Eric Smith <[email protected]> > wrote: > >> Interesting. Lack of global awareness duly noted. >> >> But also, can you check me on this?: >> >> > On Dec 26, 2022, at 7:21 PM, glen <[email protected]> wrote: >> > >> > This exchange was interesting. I've never seen ⊃° used. >> > >> > ⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄⋄ >> > me: What is the difference between ⊃ and ⊢. >> > >> > gpt: The symbol "⊃" is the logical symbol for "implies." It is used to >> form conditional statements in which the formula on the right is true only >> if the formula on the left is true. For example, the formula "A ⊃ B" can be >> read as "A implies B," and it means that if A is true, then B must also be >> true. >> >> Am I somehow blanking on ordinary sign-flips, or mistaking left and right? >> >> Seems B Is true _if_ A is true. B is false _only if_ A is false == If A >> is true, then B must also be true. >> >> Given that English is not ensured to have any global internal logical >> consistency, one can see making sentences that don’t close internally. But >> in areas where English is capable of being used with internal consistency, >> I am surprised to see an “only if” transposed with an “if” everywhere. Did >> I completely misunderstand what “implies” means? >> >> >> On all this I feel completely exposed: I thought I remembered from >> Quine’s little book on propositional calculus that “implies” isn’t even an >> elementary operator; only enters in a context like modus ponens for >> proofs. In first-order logic one was supposed to write expressions such as >> “B or not(A)” to mean “if A then B”. And there was some other symbol (even >> simpler than the entails) for that conditional. >> >> Eric >> >> >> >> -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . >> FRIAM Applied Complexity Group listserv >> Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom >> https://bit.ly/virtualfriam >> <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fbit.ly%2fvirtualfriam&c=E,1,FACgozR-UqqCXQNuQwGDcUKOr9F8z9par_ZMWYigt5pt0zR5SRseqvtZvhgeXNhXZtJbOBMArZ894NdK7CRcE5elLELfxS5zueuLVPCUFvPwUnQ_&typo=1> >> to (un)subscribe http://redfish.com/mailman/listinfo/friam_redfish.com >> <https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fredfish.com%2fmailman%2flistinfo%2ffriam_redfish.com&c=E,1,Yhc5E5ab9UmYYG9HMLYkBuVWFStwPqiriJeHKTJEVbJx3gSi011Mhs_3KW7idMNg-N0XMR9DgpMC7rPIdS9XeZlcJ2U4se1WrqkjRwr_&typo=1> >> FRIAM-COMIC http://friam-comic.blogspot.com/ >> <https://linkprotect.cudasvc.com/url?a=http%3a%2f%2ffriam-comic.blogspot.com%2f&c=E,1,KjGjIbhNXx_Jkk8XVQeh0lyM3M6RydNqm286xij8qR8oHoHQcqigRNdtrPlFd2b8B98pogaXmWG6I4JoFfoHshueOTb-xfV86hrPhgpGlYoxVjU,&typo=1> >> archives: 5/2017 thru present >> https://redfish.com/pipermail/friam_redfish.com/ >> <https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fredfish.com%2fpipermail%2ffriam_redfish.com%2f&c=E,1,tKP0RmBbn5aXqMMP90FfZRUgR4SeRNAbCIPIHTmOOMKvYU9wbJQX8c6NaqJZF-ALbi5h5pfwbbR6XC7VfiNBZH8WQJvHUbf391P9nkUqxn-_LgrnFkGB5kRXKEY,&typo=1> >> 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ >> > -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fbit.ly%2fvirtualfriam&c=E,1,_spTYZpBgzfulo-KvqI8rEzXQnNQEKBsbLisXTlr_mycwxyzjQtVPPo1I2aErQUHbLfg7bzp1CSukQ6vEKVwLfp3fRDVEBuHthgGKeICow,,&typo=1 > to (un)subscribe > https://linkprotect.cudasvc.com/url?a=http%3a%2f%2fredfish.com%2fmailman%2flistinfo%2ffriam_redfish.com&c=E,1,YGWVR0l_mWGwkSJgcqb-4MaGx3TabLJ_UEXMsf4RfIVpJRtH_z_87WR9YzqtbWedPsYxpzY2Yf3GoTs9r4QlS5pDCpsUsuqqStf7wZD5TgfO7B13p230BxY,&typo=1 > FRIAM-COMIC > https://linkprotect.cudasvc.com/url?a=http%3a%2f%2ffriam-comic.blogspot.com%2f&c=E,1,VZHhoxvwV3O3HoDR22IXaL0brXD2f5UITFIIRFrhhDVotM51qEn028C93zmqUufNXjGtfdN3w9mWfwXbhnL2Y4-7O_N0mAb0_vbQXKWRjEI,&typo=1 > archives: 5/2017 thru present > https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fredfish.com%2fpipermail%2ffriam_redfish.com%2f&c=E,1,JwWnj-6UkTnEBOrj37sp44TnxhxZ5pzs-MTlWtgAfQjQRxaufe58Yo48fhJwo3DKPN1ERx4ANXtSxhjsUUDsM38mkbM4nYQCIN4pmv-AUD_FxdrE-q8,&typo=1 > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ > > > -. --- - / ...- .- .-.. .. -.. / -- --- .-. ... . / -.-. --- -.. . > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://bit.ly/virtualfriam > to (un)subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > FRIAM-COMIC http://friam-comic.blogspot.com/ > archives: 5/2017 thru present > https://redfish.com/pipermail/friam_redfish.com/ > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ >
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