“Still I Look to Find a Reason to Believe”

Philosophy 1100 Hand in Today’s Work: Assigned Exercises Next Week: Title: Critical Reasoning Instructor: Paul Dickey E-mail Address: pdickey2@mccneb.edu Website:http://mockingbird.creighton.edu/NCW/dickey.htm Hand in Today’s Work: Assigned Exercises Next Week: First Editorial Analysis is Due (2-3 pages). “Instant democracy is never doable” ??? Reading Assignment for Next week Be sure you have read Chapter 3 of your text. (skip pp. 81-85 for now) 2

Chapter Two Two Kinds of Reasoning 3

Two Kinds of Good Arguments A good deductive argument is one in which if the premises are true, then the conclusion necessarily (that is, has to be) true. Such an argument is called “valid” and “proves” the conclusion. For example – Lebron James lives in the United States because he lives in Nebraska. All men are mortal. Socrates is a man. ____ Socrates is mortal. A sound argument is a valid, deductive argument in which the premises are in fact true.

Two Kinds of Good Arguments A good inductive argument is one in which if the premises are true, then the conclusion is probably true, but not always. The truth of the premises do not guarantee the truth of the conclusion. Such an argument is called “strong” and supports the conclusion. For example: Dan lives in Nebraska and he loves football, so he is a Nebraska Cornhusker fan. If offered to me before class tonight, I would have made a bet with my wife that each of you would sit in the same seat in class that you did last week. If she would have taken the bet, would I have won more money than I would have lost?

What is “Beyond a Reasonable Doubt” vs “Proof? Although standard English usage is often lax about this, technically speaking, PROOF requires a valid deductive argument. “Beyond a reasonable doubt” requires a level of evidence in an inductive argument such that if someone were to believe it were not true, they might still possibly be right, but that probability is so remote that reasonable, critical thinking, people will be satisfied to act and claim to know without a proof.

How Do Premises Support Conclusions? For an Deductive argument, premises prove or demonstrate a conclusion based on if the premises make the conclusion certainly true. Consider the argument: (P1) If it’s raining outside, the grass near the house gets wet. (P2) It’s raining outside. _________________________ The grass near the house is wet. In a Deductive argument, premises prove a conclusion based on the logical form of the statement or based on definitions. It would be a contradiction to suggest that the conclusion is false but the premises are true.

What is Logical Form? Consider the following argument: A good God cannot exist. There is evil in the world and any God who is good would not permit evil to exist. This argument can be stated as follows: (Premise 1) There is evil in the world. (P2) A God who is good would not permit evil to exist. ____ (Conclusion) A God who is good does not exist.

What is Logical Form? Note that we can symbolize this argument with variables. In this case, say for example, this argument could be represented as: G = A good God exists, E= There is no evil in the world. This argument is of the form: If G  E ~ E _____ ~G Thus, it is a valid deductive argument. This is the deductive rule of Modus Tollens. EVERY argument that can be represented in this form is valid, regardless what G and E represent.

How Do Premises Support Conclusions? For an Inductive argument, premises support (never prove) a conclusion based on how strongly the premises provide evidence for the conclusion. Consider the argument (Variation One): (P1) When it rains outside, the grass near the house only gets wet when the wind is blowing strongly from the North. (P2) The wind usually blows from the South in Omaha. ________________________ Even though it is raining, the grass near the house is not wet.

How Do Premises Support Factual vs. Normative Conclusions? In regard to evaluating Inductive support for Factual vs. Normative Conclusions, I would suggest the following two tips to keep in mind 1) Only Factual Premises support Factual Conclusions. That is, if the conclusion is factual (or descriptive), ALL premises must be factual. 2) A Normative Premise is always needed to support a Normative Conclusion. That is, if the conclusion is normative (or prescriptive), there must be at least one normative premise. Of course, there may or may not be factual premises!

How Do We Evaluate an Argument? There are generally two requirements (and only two) logically to evaluate a claim – 1) Do the premises support or prove the conclusion? Or is the argument valid (if deductive) or strong (if inductive)? 2) Are the premises true? -- It would be nonsense for you to object with, for example, “I don’t want to believe that” or “You shouldn’t say that”, or “Where did you come up with that?” “That’s not what my girl friend says,” “You didn’t explain why it is true,” etc, etc.