Page |1
BASIC DEFINITIONS IN LOGIC (Ch1.11.4)
Ch1.1. BASIC CONCEPTUALITIES AND DEFINITIONS
A. Definitions: Logic
Argument
Statement/claim/proposition
Inference
Truth value
B. Steps in Argument evaluation: 1.) Read/Understand
2.) FIND THE CONCLUSION (look for indicator words
and note inferential relations between the
statements)
3.) Put in “Standard Form” : List premises first : Premise
Premise
Premise
List conclusion last : Conclusion
1.2. RECOGNIZING ARGUMENTS
A. A Passage can be considered an Argument if there is an ATTEMPT TO PROVE
1. This requires: a.) a Factual Claim
b.) an Inferential Claim
2. Single statements, including conditional statements, are not arguments.
-- a single statement does not entail anything beyond itself
-- conditional statements can express inferences, but do not present
a factual claim
B. Conditional Statements; Typically “If…, then…” in form. Other language is also used.
1. Antecedent – “If…” part. Can express a sufficient condition
2. Consequent – “then…” part. Can express a necessary condition
C. Sufficient and Necessary Conditions:
1. Sufficient Condition: something that, by itself alone, will bring about “X”
2. Necessary Condition: something required for “X”, but not sufficient by itself alone
to produce “X”
1.3. TYPES OF ARGUMENTS
A. Deductive: An argument best evaluated using Deductive Criteria:
1.) Conclusion follows necessarily from the premises
2.) Language of Necessity
3.) Type or kind: Definition; based on Mathematics;
Categorical, Hypothetical, and Disjunctive Syllogisms;
Arguments that apply Laws of Science deductively
B. Inductive: An argument best evaluated using Inductive Criteria:
1.) Conclusion follows probably from the premises
2.) Language of Probability
3.) Type or kind: Appeals to Authority, Analogies, Generalizations,
Signs, Predictions, Causal Arguments
Page |2
1.4. LANGUAGE FOR EVALUATING ARGUMENTS
A. GENERAL CRITERIA FOR A GOOD ARGUMENT: 1) Conclusion follows from the premises
2.)Premises are IN FACT true
How to Evaluate: STEP ONE: Assume Premises “True”. Does the conclusion follow
(necessarily or probably)?
STEP TWO: Are the Premises IN FACT True?
B. LANGUAGE FOR DEDUCTIVE AND INDUCTIVE ARGUMENTS
1. Deductive Arguments
a. Good Deductive Argument:
SOUND = 1.) VALID (conclusion follows necessarily from the premises)
2.) All the premises are IN FACT true
b. Bad Deductive Argument:
UNSOUND = 1.) INVALID ( conclusion does not follow
necessarily from the premises)
or,
2,) VALID, but with FALSE premise(s)
2. Inductive Arguments
a. Good Inductive Argument:
COGENT = 1.) Strong (conclusion probably follows from the premises)
2.) All the premises are IN FACT true
b. Bad Inductive Argument:
UNCOGENT = 1.) WEAK (conclusion does NOT probably follow from
the premises )
or,
2.) STRONG, but with FALSE premise(s)
C. VALIDITY: A Truth Preserving Characteristic:
Validity is a characteristic of some deductive arguments, WHOSE FORM IS SUCH THAT
THE TRUTH OF THE PREMISES IS NECESSARILY PRESERVED IN THE CONCLUSION.
D. TRUTH VALUES AND VALIDITY/ STRENGTH
Truth Values of the statements in an argument are “MUTE”
with respect to Validity or Strength, EXCEPT: ANY ARGUMENT
THAT HAS ALL TRUE PREMISES AND A FALSE CONCLUSION
IS ALWAYS INVALID OR WEAK.