Now put the course together. A charitable reading tells you what the argument is. Validity and truth and the conditional forms tell you how to judge it.
Key idea
Evaluate an argument in steps: (1) find the conclusion and premises; (2) ask whether the premises support the conclusion (valid, or strong); (3) ask whether the premises are true. A good argument passes both (2) and (3).
Why it works
Questions (2) and (3) are separate, and each can fail on its own. An argument with true premises can still fail to support its conclusion, and a perfect link can start from a false premise. Asking them separately tells you exactly what is wrong, which is more useful than "I disagree."
- Identify: conclusion, premises, any unstated premise (charitably).
- Link: deductive? check validity. Inductive? check strength. Watch for named fallacies.
- Truth: are the premises true, as far as you can tell?
- Verdict: good (sound or cogent), or say which step fails.
Worked example: A good argument
Evaluate: "All mammals breathe air. Whales are mammals. So whales breathe air."
- Conclusion: whales breathe air. Premises: all mammals breathe air; whales are mammals.
- Link: "All B are C; A are B; so A are C" is valid.
- Truth: both premises are true.
Answer: Sound: a good argument.
Worked example: Which step fails?
Evaluate: "All birds can fly. Penguins are birds. So penguins can fly."
- Link: same valid form as before.
- Truth: "All birds can fly" is false.
Answer: It follows, but a premise is false: not sound.
Common mistake
Jumping to "I disagree with the conclusion" without asking the two separate questions: does it follow, and are the premises true? Disagreeing with a conclusion tells you to look closer; it does not tell you which step is wrong.