Sir Arthur Conan Doyle created the fictional and brilliant, London-based "consulting detective", Sherlock Holmes. Holmes is famous for his astute logical reasoning.

"All emotions were abhorrent to his cold, precise but admirably balanced mind."

If we take to heart what many of you have said in class; Reason is the most reliable Way of Knowing. In fact, some of our TOK students have suggested that it is the only valid Way of Knowing if our goal is to find justified, true belief. And weak and unreliable emotion sits on the sidelines for many of you as a poor relative to our serious and pragmatic reason. Perhaps we will reconsider these conclusions if we take to heart some words of Arthur Conan Doyle via Holmes: "It is a capital mistake to theorize before you have all the evidence. It biases the judgment".

Reason is the use of the mind in a logical manner and is a powerful way of knowing. We use reason all the time. Rational thinking can lead to clarity and important truths. There are rules and order to rational thinking and this is often a comfort to many of us (an emotional response to reason?). Something like deductive reasoning can be as Holmes might say, elementary.

If A=B

and B=C

Then A=C

What the syllogism above implies is that If I know two true things, I can come to know a third truth just through thinking! This is really amazing. If you embrace reason as a primary way of gaining knowledge, then you are a Rationalist and you believe in Rationalism, in which knowledge comes to us mostly through the rules and applications of logic and reason. There are some problems with this position though, as a logical argument can be both valid and incorrect at the same time.

One of the problems we will consider in this unit is that many claims appear to be valid at first glance or present themselves in a manner utilizing valid reasoning but the claims just don't hold up to scrutiny.

Read the Calivn and Hobbes cartoon. Analyze the claims of the father and determine whether or not it is internally consistent. No? Yes? Are these claims true?


Consider the following quotations. As you do so, try to understand exactly what was meant by the quotation and what the implications are if such claims are true.

  1. He that will not reason is a bigot; he that cannot reason is a fool; and he that dares not reason is a slave. (William Drummond)

  2. The reasonable man adapts himself to the world; the unreasonable man persists in trying to adapt the world to himself. (George Bernard Shaw)

  3. People generally quarrel because they cannot argue. (G.K. Chesterton)

  4. You are not thinking, you are jus being logical. (Niels Bohr to Albert Einstein)

  5. The head is always fooled by the heart. (La Rockefoucauld)

  6. You do not reason a man out of something he was not reasoned into. (Jonathan Swift)

  7. Cogito ergo sum-I think, therefore I am (René Descartes)

  8. Man has such a predilection for systems and abstract deductions that he is ready to distort the truth intentionally, he is ready to deny the evidence of his senses only to justify his logic (Fyodor Dostoevsky)

  9. LOGIC, n. The art of thinking and reasoning in strict accordance with the limitations and incapacities of the human misunderstanding. (Ambrose Bierce)

Discussion Posting

  1. Write a thoughtful response (around 250-300 words) to the task below in your class discussion page in the toolbar on the left.
  2. Comment on at least two other responses. One of your comments must be to a response without any comments. Make this something more substantial than, "Great Response!"

  • Choose one of the quotes above (from our class discussion) and explain A) what you think the author intended to say and B) the implications of this truth on our daily lives.

Lesson 1: Deductive Reasoning

Lesson 2: Inductive Reasoning

Lesson 3: Logical Fallacies

Lesson 4: Problems of Reason, Lateral Thinking and Other Thoughts

Lesson 5: Intuition

Reason WOK Vocabulary:

ad hominem, argument ad ignorantiam, begging the question, belief bias, binary thinking, circular reasoning, confirmation bias, contradiction, deduction, double standards, enthymeme, equivocation, fallacy, false analogy, false dilemma, hasty generalizations, induction/inductive inference, infinite regress, lateral thinking, laws of thought, loaded questions, post hoc ergo propter hoc, premise, prison of consistency. quantifier, rationalization, rhetoric, special pleading, syllogism, validity, venn diagram, vested interest, vicious circle

TOK Lexicon of all our vocabulary