A philosopher who cannot evaluate an argument is a philosopher with only half a brain.
Evaluating an Argument
The strength of an argument lies in the support provided by the premise of its conclusion.
Where does strength lie? Deductive Lies in form; premises must have complete evidence to prove conclusion Inductive Lies in content; premises’ support ranges from little support to high probability
What happens when you add a relevant premise? Deductive Nothing Inductive The support for the conclusion will be stronger
What’s in the conclusion? Deductive Content of the conclusion is found in premises Inductive Content of the conclusion goes beyond the premises
What do the premises do? Deductive Prove the truth of the conclusion with certainty Inductive Establish the conclusion as having a high probability of being true
STEP 1: CLEAR UP THE CONCLUSION! What does the conclusion want to prove? Are the premises relevant to it?
FALLACY OF IRRELEVANT REASON • Premise is irrelevant to the conclusion and holds no support Example: I watch Power Rangers; therefore, I am a Power Ranger.
STEP 2: TEMPORARILY ASSUME THE PREMISES TO BE TRUE/FALSE! What happens when you manipulate the truth of the premise set? Did it weaken the support to the conclusion? Strengthen it? What kind of support was given?
STEP 3: CHALLENGE THE TRUTH OF THE PREMISES! Demonstrate that at least one of the premises is false. Demonstrate that the truth of one of the premises is difficult to establish with certainty.
A-form and E-form statements are easy to falsify and difficult to verify: A-form: “All x is y.” E-form: “No x is y.” One false premise falsifies the entire premise set. A false premise set mean no support for the conclusion.
STEP 4: CHALLENGE THE TRUTH OF THE CONCLUSION! One way to do so is by using a counterexample. Demonstrate that the truth of one of the premises is difficult to establish with certainty.
Look out for the following words in claims: SOME – safe choice MOST – 50% +1 ALMOST ALL – ~80% ALL – 100% “Almost all” claims can be falsified by several counterexamples. “All” claims can be falsified by one counterexample.
PRACTICE TIME. 76%? 85%? 57%? 99%?
DEDUCTIVE ARGUMENTS Pro tip: To attack a deductive argument, Test the truth of the premises All humans are mortal. Diego Silang is human. Therefore, Diego Silang is mortal. WEAK
INDUCTIVE ARGUMENTS Pro tip: Use “Many” instead of “Most” Apolinario is a UP batch 2000 freshman and comes from a poor family. Andres is a UP batch 2000 freshman and comes from a poor family. Douglas is a UP batch 2000 freshman and comes from a poor family. WEAK All UP batch 2000 freshmen that I know come from poor families. I have found no conflicting case. Therefore, most UP freshman batch 2000 come from poor families.
TIP: More relevant premises = higher probability = stronger support Most UP freshmen batch 2000 come from poor families. Jumanji is a UP freshman batch 2000. 85% of freshmen enrolled in Math 17 are from poor families. Therefore, more likely than not, Jumanji comes from a poor family. Jumanji is enrolled in Math 17.