Evaluating Arguments Jason M. Chang Critical Thinking

Lecture Outline Background A condition R condition G condition Using the ARG conditions

Background Evaluating arguments Evaluating arguments involves determining whether the argument is “good” (i.e., “sound” or “cogent”)

Background How to evaluate Use criteria to determine whether the thing being evaluated is “good” or “bad” Examples? Examples of evaluating something Evaluating a restaurant Good food Good service Clean and sanitary Reasonable pricing

Three criteria for evaluating arguments Background A – Acceptable premises R – Relevant premises G – Good grounds Three criteria for evaluating arguments

(A) Acceptability of Premises A good argument must have acceptable premises (P1) All women are rich. (P2) Socrates is a woman. Therefore, (C) Socrates is rich. (P1) If we allow same-sex marriage (SSM), society will collapse. (P2) We’ve allowed SSM. Therefore, (C) Society will collapse. Does not matter how impeccable the logic is (P1) Either you attend church or you are an evil person. (P2) You don’t attend church. Therefore, (C) You are an evil person.

(A) Acceptability of Premises Acceptability VS. Truth Why does the book use acceptability instead of truth? Does not matter how impeccable the logic is

(A) Acceptability of Premises Acceptability VS. Truth Reason #1: A premise can be acceptable without knowing it is true (P1) It will rain tomorrow. Therefore, (C) You should set out your jacket Does not matter how impeccable the logic is

(A) Acceptability of Premises Acceptability VS. Truth Reason #2: A premise can be acceptable without it being true for everybody (P1) We should choose a destination that has _______. (P2) Hawaii has _______. Therefore, (C) We should go to Hawaii. Example – convincing the family that annual vacation should be in Hawaii this year (P1) We should choose a destination that has _________. (P2) Hawaii has ____________. Therefore, (C) We should choose Hawaii   Wife – good shopping Brother – good food Teenage son – good surfing Teenage daughter – hot guys Ethical question Is it ethical to use knowingly false premises to argue for something?

(A) Acceptability of Premises Acceptability VS. Truth Reason #3: Charity (P1) The archaeopteryx’s main feathers show the asymmetric, aerodynamic form typical of modern birds. (P2) The asymmetric, aerodynamic form of feathers is evolved to aid in flying. Therefore, (C) The feathers of the Archaeopteryx must have been used for flying.

(R) Relevance of Premises A good argument must have relevant premises A premise is relevant to the conclusion if it provides some evidence or reason for the conclusion

(R) Relevance of Premises Relevant premises? (P1) Smith has an appendicitis, gout, and bladder cancer. Therefore, (C) Smith is not healthy enough to run a marathon. (P1) Basketball is a game in which height contributes toward one’s success. Therefore (C) Basketball is a game for which physical characteristics make a difference

(R) Relevance of Premises Same subject does not necessarily suggest relevance (P1) I went to the party. Therefore, (C) The party was fun (P1) Philosophy is fun. Therefore, (C) Philosophy is difficult.

(R) Relevance of Premises Relevance does not necessarily suggest enough support (P1) Guns are the cause of tens of thousands of deaths each year. Therefore, (C) We should ban guns. (P1) I attended and participated in every class. Therefore, (C) I should pass the class. 30,000-35,000 gun deaths in the U.S.

(G) Good Grounds (P1) Guns are the cause of tens of thousands of deaths each year. Therefore, (C) We should ban guns. (P1) I attended and participated in every class. Therefore, (C) I should pass the class. It is possible have relevant premises that fail to give enough support for the conclusion

(G) Good Grounds A good argument must have premises that give good grounds for the conclusion Premises give good grounds for the conclusion if they provide enough support for the conclusion NOTE: If the premises give good grounds, they must be relevant (but not vice versa).

(G) Good Grounds Form of argument Arguments that use information (e.g., numbers, statistics) How it can fail G Fails to account for all relevant information (P1) Cars are the cause of over 35,000 deaths each year in the U.S. Therefore, (C) We should ban cars.

(G) Good Grounds Form of argument Arguments that make a generalization from a sample How it can fail G Inadequate sample (e.g., small sample size) (P1) I met 3 Parisians in my life. (P2) All 3 smoked. Therefore, (C) All Parisians smoke.

(G) Good Grounds Form of argument Arguments that derive cause from effect How it can fail G Fails to account for all possible causal factors (P1) The two boys behind the Columbine school shooting were fans of The Matrix. Therefore, (C) To protect our children, The Matrix should removed from video store shelves.

Using the ARG conditions

Using the ARG Conditions Evaluating arguments Check the premises for their acceptability Check the premises for their relevance to the conclusion Check the premises to ensure they give goods grounds for the conclusion If all three, the argument is cogent

Using the ARG Conditions (P1) (P2) So, (P3) (P4) Therefore, (C) Arguments with subarguments The subargument must also meet ARG Subarguments must be evaluated independently from the main argument Must meet ARG Must meet ARG

Using the ARG Conditions If the argument meets all ARG, you are rationally committed to accepting the conclusion An argument can fail the ARG even if you the conclusion is true