About True Sentences and Decisions

Abstract

Introduction:  In the episode concerning the riverboat trip, Lisa and her classmates are dealing with the question of what makes sentences true.  Three different ideas are exemplified.  First, during a boat trip, Mark throws some water on Harry in order to make him agree that the sentence "water is wet" is a true sentence.  Harry does agree with Mark, noting that "sentences are true when they correspond to facts."  Second, Tony tells he has dreamed he was in China.  It seemed to him it was reality.  When asked about how he is sure that it was just a dream and not reality, he answers that he couldn't have been in China without having traveled there first, and he knew he had not traveled.  He says it would not have been consistent to have been in China without having traveled there.  He says, "What happened in the dream was not consistent with everything else in my life.  It wasn't consistent, so it wasn't true."  Third, some of the kids get lost.  While discussing what they should do to find their way again, three ideas were given: to use a compass, (which was impossible since none of them had brought one), to look on a map (which was also impossible for the same reason), and to follow the stream they were facing, in the hope that it flew to the river, where they had been earlier so that they could see where they had to go.  Since they all agreed this idea was worth trying, . . . "the six of them walked along the bank of the stream."  As it came out, it worked well.  They did get to where they wanted.  From this they learn that sometimes to decide (know) whether a given sentence is true or not, one has to test the idea and check over if it works or not.  It works only if it is true.