T H E C O N S T R U C T I O N O F A F O R M A L A R G U M E N T

LOGIC

LOGIC: THE STUDY OF THE CORRECT RULES OF REASONING

• Reason vs. Rhetoric• Propositions: declarative statements that assert a

claim• They are either true or false

• Analytic vs. Synthetic propositions (Kant)• analytic: predicate adds nothing to the subject• E.g. 2 + 2=4• Deductive reasoning• Pure rationalism; no new information from the world

• Synthetic: predicate adds knowledge to subject. • Conclusions come from our observation of the world• E.g. “The rose is red.”

INDUCTION

• Drawing conclusions from observation of particular cases• Scientific method• Knowledge is always a matter of probability• We frame expectations of future events

• Arguments not “valid” in formal sense; rather, “strong” or “weak”

• Analogical reasoning (“if it cures cancer in mice, it should cure cancer in people”)• Occam’s Razor

ABDUCTION

• Reasoning “to the best explanation”• Seeks to add explanatory reason• “Occam’s razor”• Seek simplist explanation

• Is there a God? (utilizing abductive reasib)

DEDUCTIVE REASONING{DEDUCE: TO DERIVE A CONCLUSION FROM SOMETHING

KNOWN)• Syllogisms: formal arguments with premises and conclusions• Truth preserving (as in a mathematical equation)• Validity vs. soundness

• A valid and sound argument should always be true• Categorical syllogism• A) Socrates is a man• B) All men are mortal• C) therefore: Socrates is mortal • (valid & sound argument)

• A) Socrates is a dolphin• B) All dolphins are mortal• C) Therefore: Socrates is mortal • (valid but unsound)

HYPOTHETICAL SYLLOGISM FORMS

• Modus Ponens: (affirming the antecedent)• If P, then Q• A) If it rains the ball game will be cancelled• B) It’s raining• C) the game is cancelled

• Modus Tallens (denying the consequent)• If P, then Q; Not P; not Q• A) If it rains the ball game will be cancelled• B) It is not raining• C) the game is not cancelled

INVALID HYPOTHETICAL FORMS

• Denying the antecedent • A) if P, then Q• B) not P• C) therefore, not Q

• Example• A) If Mary is a mother, she is a woman• B) Mary is not a mother• C) Therefore, Mary is not a woman

INVALID HYPOTHETICAL FORMS

• Affirming the consequent• A) If P, then Q• B) Q• C) therefore, P

• Example:• If Mary if a mother, she is a woman• Mary is a woman• Therefore, she is a mother

NECESSARY VS. SUFFICIENT

• Necessary—”A” is required for “B” result• (To earn good grades one must study diligently)

• Sufficient—”A” is one cause of “B” result• (beheading is sufficient for death)

• Necessary and sufficient• (For the world to be made right, Jesus must return)

LOGICAL FALLACIES: A LIFELONG PURSUIT