Ch.3 Flashcards
Argument basics
•Deductive: Intended to provide logical conclusive support for a conclusion.
•Inductive: Intended to provide a probable support for a conclusion.
Deductive argument
•Valid: A deductive argument that succeeds in providing conclusive support for Conclusion.
•Invalid(Unsound): A deductive argument that fails to provide conclusive support for its conclusion.
•Sound: A deductively valid argument with true premises.
•Truth-persevering: Valid argument is such that if it’s premises are true, it’s conclusion must be true.
•Validity: about structure of argument to the premises guarantee truth of conclusion if true?
•Soundness: about truth of premises but can only apply to arguments that are valid. 
Sound argument examples
- humans are mortal
- Socrates human
- therefore, Socrates is mortal.
Valid arg form. Also true premises so therefore sound
Invalid (unsound) example
1.All dogs are mammals
2.All cows are mammals
3.Therefore, all dogs are cows.
Even if promises are true, the conclusion could still be false. The truth of premises doesn’t guarantee truth of the conclusion. So deductively invalid. If an argument is invalid, it can’t be sound, even if the premises are true.
Valid but unsound example
- All humans are Immortal
2.Socrates is human
3.Therefore, Socrates is immortal.
Valid, if premises were true, conclusion would be true. But unsound humans aren’t immortal. Correct argument structure ,false premise.
Unsound (invalid and fake premises)
1.All dogs are reptiles
2.All cows are reptiles
3.Therefore, all dogs are cows
Invalid argument structure and false premises
Inductive argument
•Strong: Succeeds in providing very probable support for its conclusion.
•Weak: Fails to provide very probable support for conclusion
•Cogent: Inductively strong argument with true premises.
•Inductively strong: if promises are true conclusion is very likely true.
Assessing both kinds of arguments
Deductive argument: Are either valid or not. 
•Validity
•Soundness
Inductive argument: The strength and weakness of inductive arguments is a matter of degree. Can be stronger or weaker.
•Strength
•Cogeny
Inductive argument example
1.98% of dogs have fleas
2.Therefore, my dog probably has fleas
Strong if premises is true, the conclusion is very likely to be true. But promises is false so it’s not cogent. 
Inductive argument example 2
1.We have observed millions of swans and have all been white.
2.Therefore all swans are probably white
Strong and cogent. But conclusion can still be false Inductive arguments only make Conclusions very probable not absolutely true. 
Judging arguments
4-Step procedure
1) Find conclusion and then premises
2) Ask: Must conclusion be true it’s premises are true,
-If so, it’s deductive
3) Ask: must conclusion probably true if premises are true?
-If so, it’s inductive
4) Ask: Is the argument intended to offer conclusive or probable support for its conclusion but failed to do so?
-If so, then it’s invalid or weak (respectfully)
Indicator words for Deductive or inductive arguments
• It necessarily follows that, it logically follows that, absolutely, necessarily, certainly (Deductive)
• Likely, probably, chances are, odds are, it is Plausible that (inductive)
Finding missing parts
3-Step Procedure
1) Search for a plausible, fitting promise that makes argument valid.
2)Search for a Plausible, Fitting premise that makes argument a strong as possible
3)Evaluate the reconstituted argument
Finding missing parts example
1.Easy availability of assault rifles in the US has increased the risk of death and injury for society as a whole.
(2. Anything that increases the risk of death an injury for society as a whole should be banned.)
3.Therefore, assault rifles should be banned.
Valid argument forms
+
Parts of a conditional
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Syllogism 
• Certain forms are valid and invalid so if you see these forms or set up an argument this way you don’t have to check for validity on your own.
•if Price of a stock drops, then you ought to buy it. Antecedent comes first (if…drops). Consequent is what follows (you… buy it) antes means before.
•A syllogism is a detective argument made up of 3 statements 2 premises and 1 conclusion

Valid argument patterns
Affirming the antecedent (modus ponens)
If p, then q.
P.
Therefore, q.
Denying the consequent (modus tollens)
If p, then q.
Not q.
Therefore, not p.
Hypothetical syllogism
If p, then q.
If q, then r.
Therefore, if p, then r.
Disjunctive syllogism
Either p or q.
Not p.
Therefore, q.
Invalid argument patterns
Affirming the consequent (invalid)
If p, then q.
q.
Therefore, p.

Denying The antecedent (invalid)
If p, then q.
Not p.
Therefore, not q. 
What is this?
1.Either we evolved by blind, unguided processes or we were created by God.
2.We didn’t involve my blind, unguided processes.
3.Therefore we were created by God.
•Disjunctive syllogism, valid
•Can’t attack argument by questioning it’s logical form.
•It’s presented in valid argument form.
•If you were going to attack, you’d have to challenge the truth of its premises (and so it’s soundness)
What is this?
1.If we have free will, then we are morally responsible.
2. We don’t have free will.
3. Therefore, we are not morally responsible.
Invalid denying the antecedent
Diagraming arguments
5-Step Procedure
1) Underline the premises and conclusion indicator words and the number the statements.
2) Find conclusion and draw wavy line under it.
3) Find and underline premise.
4) Cross out extra material.
5) Draw arrows between premise and conclusion to show their logical connections.
Dependent and independent premises
•Dependent: Depends on at least one other premise to provide joint support for a conclusion. 
•Independent: Doesn’t depend on other premise to provide support to a conclusion.
•Removing a dependent undermines the support that it’s linked dependent premises supply to conclusion.
Assessing long arguments
4-Step Procedure
1)Study the text thoroughly until you understand it.
2)Find conclusion.
3)Identify premises.
4)Diagram argument.
Obstacles
•Only a small portion of prose may be devoted to premises and conclusion
•Premises or conclusion may be implicit.
•many works claiming to be filled with arguments contain few arguments or none at all. 
Counterexample method
•Technique for testing an arguments for validity.
•Try to devise an argument with the same form as test argument but with true premises and a false conclusion.
•If such an argument can be devised, the testing argument is invalid.
