Chapter 3 Flashcards
Conditional statement
If ‘p’ then ‘q’ : Asserts that something is true based on a certain condition
Antecedent
The “p” in the conditional statement formula - where “q” is claimed to be true
Consequent
The “q” in the conditional statement formula - what is claimed to follow if ‘p’ is true
Deductive argument
Claims that the premises provide logically conclusive support for the conclusion
VALID or INVALID
Inductive argument
Claims that the premises provide probably support for the conclusion
STRONG or WEAK
Valid argument
A deductive argument that succeeds in providing conclusive support for its conclusion
Invalid argument
A deductive argument that fails to provide conclusive support for its conclusion
Sound argument
Deductively valid argument with true premises
Truth-preserving
Defining characteristics of valid deductive argument: their structure guarantees that if the premises are true so also are the conclusions
Strong argument
Inductive argument that provides highly probable support for its conclusion
Weak argument
Inductive argument that fails to provide strong support for its conclusion
Cogent argument
a strong, inductive argument with all premises true
Dependent premise
Must be combined with one or more other premises to support the conclusion
Independent premise
Provides support for the conclusion on its own
Syllogism
Deductive argument consisting of two premises and one conclusion
Common valid deductive forms
- Affirming the antecedent 2. Denying the consequent 3. Disjunctive syllogism 4. Hypothetical syllogism
Affirming the antecedent
if ‘p’ then ‘q’, ‘p’; therefore ‘q’ If Spot barks, a burglar is in the house. Spot is barking. Therefore, a burglar is in the house.
Denying the consequent
If ‘p’ then ‘q’, not ‘q’; therefore not ‘p’ If it rains, the sidewalk gets wet. But the sidewalk’s not wet. So, it must not have rained
Disjunctive syllogism
Either ‘p’ or ‘q’, not ‘p’; therefore ‘q’ The number 3 is either even or odd. However, it is not even. Therefore, it is odd
Hypothetical syllogism
If ‘p’ then ‘q’, if ‘q’ then ‘r’; therefore if ‘p’ then ‘r’ If Guy steals the money, he will go to jail. If Guy goes to jail, his family will suffer. Therefore, if Guy steals the money, his family will suffer.
Common invalid deductive forms
- Affirming the consequent 2. Denying the antecedent
Affirming the consequent
Invalid deductive form If ‘p’ then ‘q’, ‘q’; therefore ‘p’
Denying the antecedent
Invalid deductive form If ‘p’ then ‘q’, not ‘p’; therefore not ‘q’ “If today is Tuesday we have logic class. Today’s not Tuesday. Hence, we don’t have logic today.”
What do good arguments do?
Appeal to reason - they show that it is reasonable to accept the conclusions given the premises
Two forms of agrument
- Deductive argument 2. Inductive argument
Example of deductive arguments
“Im taller than Aimee. Aimee is taller than Melissa. So I’m taller than Melissa.’ -> If the premises offered really are true, then the conclusion must also be true
A rule in invalid arguments?
It is a deductive argument that fails to provide conclusive support for its conclusion. ALTHOUGH - It is still possible for the premises to be true and yet the conclusion to be false.
How to evaluate soundness of an argument
- Are the premises true? 2. Do those premises lead to the conclusion?
Example of false premises that still support the given conclusion.
Pigs have wings (P). Any animal with wings can fly (P). So, pigs can fly (C). This argument is VALID but UNSOUND.
Example of true premises that don’t support the conclusion
Birds have wings (P). Bats have wings (P). Therefore, birds are bats (C).
Is the conclusion guaranteed in inductive reasoning?
No. Not intended to be
Induction
The process of building inductive arguments
Cogency
An inductively strong argument with true premises is said to be cogent. (Like the soundness of deductive arguments)
4 Steps in judging arguments
- Find the arguments conclusion and then premises. 2. “Is it the case that if the premises are true then the conclusion must be true?” -> if yes: VALID DEDUCTIVE -> if premises are true: SOUND -> Instances where the premises are true while conclusion is false: INVALID (then go to step 3) 3. “Is it the case that if the premises are true, its conclusion is probably true?” ->if yes: Inductively strong -> are premises probably true?: Cogent too -> if NO: go to step 4 4. “Is the argument intended to offer (a) conclusive or (b) probable support for its conclusion (but fails to do so)?” -> If (a): invalid deductive argument ->If (b): weak and inductive argument
Deductive indicator works
absolutely, certainly, it necessarily follows
Inductive indicator words
Probably, likely, odds are, chances are
Steps to finding missing premises
Step 1: Search for credible premises that would make the argument valid Step 2: Search for a credible premise that would make the argument as strong as possible Step 3: Evaluate the reconstructed argument
Example of a conditional statement
“If I won the lottery then I’d pay all my debts”
Argument flow charts
Always flow downward on the page (Premises at top, conclusion on the bottom) Boxes: Premises Circles: Conclusion Arrows: Connect them
Diagramming independent premises
Diagramming dependent premises
Multi-staging of arguments
Assesing long arguments - 4 steps
- Study the text
- Find the conclusion
- Identify the premises
- Diagram the argument
