Sage Training – Week 5. Assumptions and Truth Vs Validity

LSAT PREP Sage Training – Week 5 Assumptions and Truth Vs Validity: Assumptions:    What are assumptions? o Premises that the author left out of the argument. Example: o The state of Qari is hostile to our national interests. The state of Qari harbors many rare and desired natural resources. Therefore, we should invade and occupy the state of Qari.  Assumptions:  What are statements that would support the conclusion that the author left out? o Invaders of a country often gain access to the country’s natural resources.  We are assuming this. Some assumptions are logically sufficient, some are necessary, and some are neither. Good vs Bad Arguments:   When we say that an argument is good we mean: o Describes how well the premises support the conclusion. o Strength of the support of the relationship between the premises and the conclusion. o Few reasonable assumptions are a good argument. When we say that an argument is a bad argument we mean: o Terrible: lots of or unreasonable assumptions. o Bad: some assumptions are questionable. o Make many and highly uncertain assumptions. o Premises weakly support their conclusion. Assumptions are Subtle:   Subtle things are hard to notice. Supposed to be sensitive to assumptions, they determine whether arguments are good or bad. Validity vs Truth:    Pretend all premises are true. Then ask yourself if the conclusion must also be true? o Yes – argument is valid. o No- argument is not valid. Example:    o All Jedi use force. Luke Skywalker is a Jedi. Therefore, Luke Skywalker uses the force.  Both premises are true.  Conclusion is also true. Notion of Validity: o What makes a good argument?  Best arguments are ones with the strongest support relationships possible between the premises and conclusion.  Zero assumptions being made. o Example:  All Gerbils are yeoogh. Darth Vader is a gerbil. Therefore, Darth Vader is a yeoogh.  All three sentences are false.  Is the argument valid? o Pretend all premises are true. o The conclusion must also be true. Validity is a special relationship between premise and conclusion. o Validity is the strongest of the support relationships. Valid Argument – if the premises are true, then the conclusion must also be true. Truth:  Property of sentences, declarative statements.  False statements are lies.  Example: o All dogs go to heaven.  This is true all dogs go to heaven. Validity:  Property of arguments.  Not a property of statements.  Example: o Number 2 is happy.  You can’t say this. It doesn’t make sense. Emotional states are not numbers.  Arguments can’t be true or false.  If or pretend that all premises are true, and when that’s the case then the conclusion must also be true. Common Valid Argument Forms:  There are millions of valid arguments.  Common valid argument forms. Can invent many arguments. o Affirming the Sufficient:  All boys like to play computer games. Tom is a boy. Therefore, Tom likes to play computer games.  A–B  Argument is valid because of virtue of form that it has taken.  A – B = All boys (A) like to play computer games (B).  C – A = Tom (C) is a boy (A).  C – B = Therefore, Tom likes to play computer games. o The Transitive:  Everyone has the capacity to love. Having the capacity to love requires compassion. Therefore, everyone has compassion.  A–B–C  A–C o Denying the Necessary:  All doctors treat patients. Hercules does not treat patients. Therefore, he is not a doctor:  A–B  /B  /A