MODR 1770 Oct 15/12
CH 3 – Making Sense of Arguments Lecture + Notes
D EVISING AN ARGUMENT
To show that a statement/claim is worthy of acceptance ©
E VALUATING AN ARGUMENT
To see whether the argument shows that the statement (conclusion) is worthy of
2 forms of arguments
Provides logically conclusive, absolute support for conclusion
Valid: if premises are true, conclusion must be true
o Deductively valid arguments are truth-preserving; conclusion follows
logically, order of premises makes no difference
Sound: premises are true.
Invalid: conclusion doesn’t follow logically from the premises (regardless of order of
o Argument w/ true conclusion can be invalid if conclusion isn’t supported by
Valid deductive argument; conclusion is false; thus 1 of the premises is false
Provides probable (not conclusive) support for conclusion
Cogent: has true premises
Refers to the construction of an argument; the way the premises and conclusion
*Persuading is not the same as reasoning with crit. thinking; persuading: influence
opinions by using words to appeal to their ego, gullibility, greed, anger, etc; emotional
language, psychological ploys, lies, etc. Does not show that a belief is true/warranted.
Crit. thinking reasoning can be psychologically compelling but the 2 have different
functions. MODR 1770 Oct 15/12
1. Find conclusion then premises of argument.
2. If the premises are true, the conclusion MUST be true? (Yes: deductive)
a. Check to see if it’s sound (valid).
3. If the premises are true, is the conclusion PROBABLY true? (Yes: inductive)
a. Check to see if it’s cogent (strong).
4. Is the argument intended to offer conclusive/probable support but fails?
(Invalid/weak argument; determine what kind of argument is intended)
a. If form shows it’s inductive/deductive, assume it’s intended
b. If indicator words (form shows no clues) shows it’s inductive/deductive,
assume it’s intended
i. Deductive: absolutely, necessarily, certainly
ii. Inductive: plausible that, probably, odds/chances are
F INDING MISSING PARTS
Some premises are implicit/assumed and left out
Often these are controversial and must be examined
Find an unstated premise when something essential is missing that’s not a
common sense generally accepted assumption.
Usually left out/downplayed to make an argument seem stronger.
T O MAKE SURE INVESTIGATION OF IMPLICIT PREMISES IS THOROUGH &
1. Search for credible premise that would make argument valid & provide link
between premise(s) & conclusion.
a. Is the most plausible & best fits with author’s intent (Principle of
Charity (in interpretation)
b. When we find someone’s meaning unclear, should attempt to interpret
it in a way that makes sense
2. (If step 1 doesn’t work)
Search for credible premise that would make argument as strong as possible &
fits with the principle of charity
3. Evaluate reconstructed argument. MODR 1770 Oct 15/12
Deductive Argument Patterns
INVOLVE 2 KINDS OF STATEMENTS :
If p, then q
Compound statements composed of 2 parts:
o Antecedent – follows “if”
o Consequent – follows “then”
Either p or q
Compound statement composed of 2 disjuncts
A FFIRMING THE A NTECEDENT (M ODUS PONENS )
Valid; deductive, conditional.
If p then q.
Not necessarily sound (premises could be false)