Week 3: Practical Rationality

Forms of reasoning

Example: joining Zip.ca.


Deduction: if p then q, p, therefore q.

Inductive generalization: Many X are Y, so maybe all X are Y.

Inference to the best explanation: Hypothesis H is a better explanation of phenomena P than available alternatives, so maybe H is true. Explanatory coherence.

Reasoning based on probabilities and statistics.


Practical induction: Action A has served in the past to accomplish goal G. So A is a good way to do G.

Inference to the best means: Action A is the best available way to accomplish G, so maybe I should do A.

Deliberative coherence: Action A fits best with all my goals, so I should do A.

Mathematical decision theory (see week 5).

Procedural/substantive dispute: Can we legitimately argue about ultimate goals?

What is the relation between theoretical and practical rationality?

Four possibilities:

1. They are independent of each other.

2. Theoretical rationality depends on practical rationality: Theoretical reason is justified because it helps us to accomplish our practical aims.

3. Practical rationality depends on theoretical rationality: Practical rationality is justified because we have good reasons to believe that making decisions based on reason is effective.

4. They are mutually interdependent - coherent.

Discussion Questions for Week 4

  1. What contribution does the history of philosophy make to philosophy?
  2. What are the main differences between Humean and Kantian conceptions of rationality?
  3. Which conception do you find most plausible?
  4. What does Smith think is the most plausible Humean view of the relation between reasons and practical rationality?
  5. How does the categorical imperative contribute to practical rationality?
  6. What is the relation between practical rationality and moral reasoning?

PHIL 680

Computational Epistemology Laboratory.

Paul Thagard

This page updated Sept. 26, 2005.