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Contemporary Moral Issues, Spring 2019

Arguments

Terms:

Premise = indicated by phrases such as since, because, for, this follows from”

Conclusion = indicated by phrases such as therefore, so, thus

Validity = conclusion follows from premises

Soundness= valid AND has true premises

Deductive arguments = conclusion follows from premises with logical necessity, supposing the premises are true;

impossible to have false conclusion

Deductive argument forms:

- Modus Ponens: Premise 1. if A, then B → Premise 2. A → Conclusion: B

- Modus Tollens: P1. if A, then B → P2. not A → C. not B

- Disjunctive Syllogism: P1. A or B → P2. not A → C. B

- Hypothetical Syllogism: P1. if A, then B → P2. if B, then C → C. B

- Introduction to Conjunction: P1. A → P2. B → C. A and B

- Elimination of Conjunction: P1. A and B → C. B

- Introduction of Disjunction: P1. A or B → C. A

- Double Negation Elimination: P1. if it is not the case that it is not A → C. it is A

Inductive arguments = valid if conclusion follows with high probability (generalization); i.e.

Abductive arguments = valid if conclusion is the BEST explanation; simplicity, explanatory power, likelihood

Deductive version of inductive = sample population(S), overall population(O), property(P), distribution (D); similar to

Modus Ponens

- P1. D% off members of S have property P and S is s representative sample of O with respect to P.

- P2. If D% of members of S have P and S has a high chance of being a representative sample, there’s a high

chance that D% of O have property P.

- C. From P1 and P2 follows that there’s a high chance D% of O have P.

Is/ought fallacy = attempting to derive an evaluative fact from non-evaluative fact; i.e. P1. water is H2O → C. water is

good

- Evaluative - what ought to be, what’s valuable, what’s better; non-evaluative = doesn’t tell anything about

values

Equivocation fallacy - key term changes meaning in argument (i.e. feathers are light→ what’s light isn’t dark →

feathers can’t be dark); invalid

Reductio ad absurdum - reduces position being criticized to absurdity (false state); i.e. assume P is true → from this,

deduce that Q is true→ also, deduce that Q is false→ thus, P implies both Q and not Q (a contradiction, which is

necessarily false) → therefore, P itself must be false

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