PHIL 2020 Unit 2: Lecture 2 Basic criteria for evaluating arguments What is the goal of an argument? o To persuade the audience of the conclusions truth How does an argument try to do this? o By showing that its assumptions, its premises, make the conclusion true. Basic criteria for criticizing arguments There are two ways an argument can fail in its goals. What are they? It premises can be unreliable; that is, we can have good reason to think that they are false. Its premises can be irrelevant to its conclusion; that is, even if they are reliable, they do not provide reason to think that the conclusion is true. So arguments can be evaluated along two dimensions: reliability and relevance. Reliability = likelihood of truth What is the highest standard of reliability? o Necessity Can a reliable statement ever be false? o Yes, consider: You will not win the lottery. o This statement is reliably true for all people, but has proven false on some rare occasions. What is the lowest standard of reliability? o X > 50 Relevance = degree of support for conclusion What is the highest standard of relevance for premises in an argument? o Deductive validity Can relevant premises ever be true without their conclusion being true? o Yes, consider: Most people have never gone to outer space. John is a person, therefore John has never gone to outer space. If we were talking about John Glenn, the conclusion would be wales, but the premises still relevant. What is the lowest standard of relevance? P(A) < P(A I B), where A is the conclusion, and B is the premise. Reliability Relevance There is no inferential relationship between reliability and relevance; in other words, given that a premise is reliable, we are not able to determine its relevance, and viceversa. These properties are jointly necessary for a premise to be effective. Only if a premise is both reliable and relevant is it useful in supporting a conclusion. Good arguments can have a bad premise, just not only bad premises.