Basics-of-arguments

source = 24.09 Minds and Machines - MIT OpenCourseWare

Premise-indicators are words that usually come right before a premise and often serves as “flags” for premises. Example:

• because
• since
• given that
• for

conclusion-indicators are words that come right before the conclusion of the argument. Example:

• thus
• therefore
• it follows that
• so
• consequently

Evaluating arguments

1. A conclusion is entailed by premises if it’s impossible for all the premises to be true while the conclusion is false. In other words, if all the premises are true, the conclusion must be true
2. an argument is valid if the conclusion is entailed by the premises
3. a deductive argument is sound if the argument is valid and all its premises are true
4. the conclusion of a sound argument is true

Argument-forms and common flaws

Argument name	general form
Modus ponens	- If p then q - p - hence, q
Modus tollens	- if p then q - not-q - hence, not-p
Disjunctive syllogism	- either p or q - not-p / not-q - hence q / p
Categorical syllogism	- All p’s are q’s - x is (an) p / all q’s are r - x is q / all p’s are r

flaws	meaning
fallacy of equivocation	using key terms in different senses in different parts of the argument
begging the question or circular argument	assuming what you are trying to prove. A weak form of this would be to put forward a premise so close to the conclusion that no one would believe the premise who didn’t already believe the conclusion
proving too much	an argument is said to prove to much if it appeals to a principle which has consequences the formulator would not accept or which are clearly wrong
Ad hominem	an ad Hominem argument involves a personal attack on one’s opponent rather than a reasoned objection to their argument
appeals to authority	it is not acceptable to support a position simply by pointing out that someone holds it
straw man argument	to represent the opponent’s position unfairly so that it is easier to shoot down