tag:blogger.com,1999:blog-19346366.post113374678634649605..comments2021-07-30T00:31:53.665-04:00Comments on Face to Face: Everyday proof techniques: by contradictionagnostichttp://www.blogger.com/profile/12967177967469961883noreply@blogger.comBlogger2125tag:blogger.com,1999:blog-19346366.post-1170151552520621532007-01-30T05:05:00.000-05:002007-01-30T05:05:00.000-05:00By the way, I don't really get the exercise -- can...By the way, I don't really get the exercise -- can I just say that we can infinitely add an and to the sentence? <BR/><BR/>It seems that we would reach a limit of intelligible sentences pretty quickly... eventually we'd have to make up redundant or gibberish sentences. Are we still dealing with sentences then?Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-19346366.post-1170151382418042252007-01-30T05:03:00.000-05:002007-01-30T05:03:00.000-05:00"If a quadrilateral x is a square, then that quadr..."If a quadrilateral x is a square, then that quadrilateral x is also a rectangle." Let's assume this statement is false -- then we grant the premises are true, but deny that the conclusion follows from them.<BR/><BR/>You have unstated premises, don't you? Kinda confuses us stupider people. ;)<BR/><BR/>My stab: <BR/><BR/>1. A all squares have 4 90-degree angles. (All S1 are S2)<BR/>2. All shapes with 4 90-degree angles are rectangles. (All S2 are R)<BR/>Then:<BR/>3. If a shape is a square, than that shape is a rectangle. (If P then Q - isn't this a premise?)<BR/>4. P<BR/>5. Q.<BR/>OR<BR/>4. Assuming ~P<BR/>5. Then ~Q<BR/>6. Then 2 and ~2??<BR/><BR/>I can't figure it out.<BR/><BR/>I haven't done formal logic in a year or so and was never very good at it to begin with. Maybe you can straighten me out.Anonymousnoreply@blogger.com