If you have read my Top 10 Lessons in Thinking, this is a deeper look. Again, the ideas are from Leonard Peikoff.

I sequenced this list so as to follow a flow. Enjoy!

1. To live man needs knowledge, and for that he needs reason.

2. Rationality is man’s most important attribute.

3. Emotions are products of ideas.

4. Wishing won’t make something so.

5. Our main choice is whether to focus.

6. A true idea is one which conforms to observations.

7. Knowledge is based on observation and logic—the art of non-contradictory identification.

8. Everything acts in a way that is consistent with its nature.

9. To be is to be something.

10. Contradictions do not exist.

11. We must carry our knowledge as a whole, with no contradictions.

12. Any statement is true, false, or arbitrary.

13. An arbitrary statement makes no attempt to connect with observation, so it cannot be evaluated.

14. We reason by abstraction—by forming concepts.

15. We form concepts by viewing concrete objects according to those similarities and differences that are essential for cognition.

16. Concepts organize observations so we can hold a large amount of relevant knowledge in our field of focus at one time. Knowledge thus held can be integrated into one’s hierarchy of other knowledge.

17. Concepts relate to one another hierarchically.

18. More abstract concepts are reducible to less abstract ones, which are reducible ultimately to observation.

19. All knowledge must be tied to observation.

20. No concept can contradict an earlier concept on which it depends. (This is the fallacy of the stolen concept.)

21. Concepts are reliable if facts of reality give rise to the need for them and if they can be integrated to our other knowledge.

22. Concepts are groupings of concretes based on our knowledge of their essential similarities.

23. “Essential” similarities are epistemological—they may change as our knowledge increases.

24. The meaning of a concept is not exhausted by its definition.

25. The concept is the particulars, viewed as units of category.

26. We can be objective in forming concepts. Objectivity is volitional adherence to reality by the method of logic.

27. Disinterest is not a feature of objectivity.

28. The process of learning and conceptualizing is called logical induction.

29. Logical induction is the identification and integration of data into valid generalizations.

30. From induced generalizations we may reason deductively. But induction precedes deduction and makes it possible.

31. Logical induction is our method of knowledge.

32. Knowledge is always of objects and of their attributes and relationships.

33. Our knowledge is contextual.

34. We need not know everything in order to know something.

35. For any claim of knowledge, all we are entitled to say is, “The facts I have observed indicate the following conclusion.”

36. No new facts contradict old knowledge. (This assumes it was knowledge.)

37. New facts change the context.

38. Within a given context, certainty is possible.

39. We are entitled to say, “Given these observations, I am certain that this conclusion follows.”

40. We must always ask, “What is the essential issue? On what fundamental principles does the question depend?”