Slide 1Slide 2Slide 3Slide 4Slide 5No new formal rules in remainder of chapter 2 . . . just learning to use the Fitch programBe sure to work through the “You try it” sections carefully (and refer to software manual) to learn how to open, construct, and save proofs in Fitch.Let’s do some proofs together …Exercise 2.5 Proving the transitivity of identity:%We are told that b = c and also that a = b. Using the first identity statement (b = c), by the indiscernibility of identicals we may substitute c for b in the second identity statement (a = b), giving us a = c and proving the transitivity of identity. Open Exercise 2.16 in Fitch and construct a formal version of the above proof. Then do 2.18 and 2.20To prove an argument invalid (i.e., to prove nonconsequence), find a counterexample showing that it is possible in some ‘world’ for all the premises to be true but the conclusion false. (cf. pp. 63-65)%Al Gore is a politician.Hardly any politicians are honest.Therefore, Al Gore is dishonest.In this course, we normally create counter-examples in Tarski’s World.Note that exercises 2.24-2.27 of your homework require you to decide whether the argument is valid or not, then respond accordingly (if valid, construct a proof of its validity in Fitch; if invalid, construct a counterexample world in Tarski’s World)Let’s do 2.25 together …Here is argument 2.25 (from p. 66 of the textbook). Is it valid? If so, we must construct a proof in Fitch. If not, we must build a counterexample in Tarski’s world:
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