Overview
This lecture explains how to classify arguments as deductive or inductive and how to evaluate their validity, strength, soundness, and cogency.
Deductive vs. Inductive Arguments
- Deductive arguments aim for their conclusions to be guaranteed if their premises are true.
- Inductive arguments aim to make their conclusions probable, not certain, based on their premises.
Evaluating Deductive Arguments
- If assuming the premises are true makes the conclusion necessarily true, the argument is valid.
- If assuming the premises are true does not guarantee the conclusion, the argument is invalid.
- Valid arguments can have false premises.
- A sound argument is both valid and has all true premises.
- An unsound argument is valid but has at least one false premise.
Evaluating Inductive Arguments
- If true premises make the conclusion probably true, the argument is strong.
- If true premises do not make the conclusion probable, the argument is weak.
- Strong arguments can have false premises.
- A cogent argument is strong and has all true premises.
- An uncogent (not cogent) argument is strong or weak but has at least one false premise.
Determining Argument Quality
- First, identify if the argument is deductive (guarantee) or inductive (probable).
- Next, evaluate the reasoning (valid/invalid for deductive; strong/weak for inductive).
- Finally, check if the premises are actually true (for soundness/cogency).
Key Terms & Definitions
- Deductive Argument — Argument aiming for a guaranteed true conclusion if premises are true.
- Inductive Argument — Argument aiming for a probably true conclusion if premises are true.
- Valid — Deductive reasoning where true premises guarantee the conclusion.
- Invalid — Deductive reasoning where true premises do not guarantee the conclusion.
- Sound — A valid deductive argument with all true premises.
- Unsound — A valid deductive argument with at least one false premise.
- Strong — Inductive reasoning where true premises make the conclusion probable.
- Weak — Inductive reasoning where true premises do not make the conclusion probable.
- Cogent — A strong inductive argument with all true premises.
- Uncogent — An inductive argument that is strong or weak but has at least one false premise.
Action Items / Next Steps
- Review the master logic flow chart for classifying arguments.
- Practice classifying sample arguments as deductive/inductive, valid/invalid, sound/unsound, strong/weak, cogent/uncogent.