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] > <mailto:[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] > > <mailto:[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/ > <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/
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