Hello, I’m Pang Ying. Welcome to Episode 21 of Think Like a Debater.

Only two episodes remain in Part Two, Building Arguments. I hope we need not squeeze in too much.

We will organize last episode’s discussion of argument, then move to today’s focus: strength and burden of proof.

Last time we divided arguments into deductive and inductive forms.

Strict definitions of deduction are somewhat disputed, but one point is not:if premises are true and logic valid, deduction preserves truth with certainty.Its conclusion contains no information beyond the premises; it merely transforms what is known.

If Teacher Pan is homeroom teacher of Class Three and Pang belongs to Class Three, deduction shows Pan is Pang’s teacher. Mathematics likewise begins from self-evident axioms and uses valid logic to derive certain conclusions.

Science also uses the hypothetico-deductive model. To overturn Aristotle’s 1,900-year claim that falling speed is proportional to weight, Galileo hypothesized that speed and weight are unrelated. Before proof, this was a hypothesis. How could an experiment test it?

If the hypothesis holds, two iron balls should land simultaneously. Drop them from the Leaning Tower of Pisa; simultaneous impact would support the hypothesis.

The deduction is: if speed is unrelated to weight, two iron balls land together; likewise an iron ball and feather fall together in a vacuum.

Induction differs and invites much dispute.

It reasons from experience to conclusions beyond known information: human nature is good, everyone has cognitive blind spots, or disadvantaged families can scarcely produce elite children. We cannot observe every person or guarantee no exception, so the conclusion makes a leap beyond the premises.

Last episode listed several methods:

1. Simple enumeration and scientific induction

2. Eliminative induction

3. Analogy

4. Statistical induction

Facts, data, mechanisms, examples, and authoritative theories all serve these methods.