Class time: 90 minutes

Goals and objectives:

Opening: 15 minutes

According to IBO, when we decide “to flow” into the area of reason in our TOK quest for different layers of knowledge, first what we have to ask ourselves is:

What is the difference between reason and logic?

How reliable is inductive reasoning? (here to add, deductive reasoning, too)

Are we predictably irrational?

But instead of searching for an answer to the very first question posted here, let`s examine the third one. Are we predictably irrational? If we ask ourselves this question in this tone, there is a slight possibility that we might loose our direction somewhere in philosophy while investigating do we construct our worldviews (and knowledge too) on reason or rather on emotions, imagination or faith, for example. If you see a person in danger, it is to expect that you won`t stay calm and rational, standing by a side of ignorance as a peaceful observer of such a scene. Perhaps you decide to help to that person. In that case, we can claim two. Or you employ your emotions and emotions work then instead of your rational thinking (“it is not useful to jeopardize my own life for the sake of rescuing of some stranger”) or you will employ your pre – rational thinking, whether we call it intuition or empathy as understood in frames of evolutionary psychology (“such an empathy has to produce some benefits for the survival of the world”).

E. Dombrowsky writes that a winner of Nobel price in economics Daniel Kahneman done significant research on how we reach our conclusions.

Kahneman, jointly with Amos Tversky explored, how he said, “the psychology of intuitive beliefs and choices and examined their bounded rationality.” According to him, intuition occupies a position between perception and later reasoning of what was perceived. Intuition is fast, automatic, effortless etc while reasoning is slower, serial.

Or to take another example: Imagine that you have a wonderful job. Suddenly, out of blue, you decide to leave it and to travel around the world on a bike. Be sure that many people, when employ their reason would consider your decision as a decision of a lunatic. However, you don`t care for any other opinion then yours. Let`s guess you are lead by your emotions.

Here to conclude, although immensely important, reason is not only way of knowing by which we construct our picture of the world. Emotions, imaginations, as sense perception a role to certain extent in above mentioned.

Let`s jump to the second question.

Development: 60 minutes

What is the difference between reason and logic?

Reason is a broader term, when comparing it with logic, that`s for sure.  Reason is, when follow Kant`s  definition, ” the power of synthesizing into unity, by means of comprehensive principles, the concepts that are provided by the intellect. That reason which gives a priori principles Kant calls “pure reason..” Difficult, eh? When “translate” Kantian language into ours, I believe that he wanted to say that reason offers to human kind a gate to understanding the essence of the world when we employ all our cognitive capabilities.

According to the Cambridge English Dictionaries, reason is:

  • the cause for something or an excuse in explanation of something 

  • the ability to think and make judgments 

Reason offers a fruitful soil for constructing and further development of logic. Logic is one of philosophical branches but it is also a branch of mathematics that deals with deductive theorems which can be proven (or disproven) absolutely. These theorems are statements that follow from each other.

If A, then B.
Therefore B.

Reasoning uses arguments when prove something. Reason does not accept claims based just on generalizations, no matter how truthful they might seem. Logic demands to be proven every statements raised.

Following activity (for students) – to watch Stephen Fry`s short explanation of philosophy, logic and reason. A short discussion on material seen is opened after that.

Rationalists versus empiricists


A discussion activity follows again. Students are encouraged to generate knowledge questions from material seen, such as, “To what extent rationalism offers certainty in constructing knowledge?”  or “Under what circumstances we can claim that empiricism is the only way for constructing pyramid of knowledge?”


  • a form of logical reasoning
  • consists of two premises (major and minor premises) and of conclusion

One of the most famous syllogisms:

  • All human beings are mortal.
  • Socrates is a human being.
  • Therefore Socrates is mortal.

Valid and invalid conclusions 

Here comes the tricky part.

The example with Socrates shows to students how they can construct their own syllogisms where both of premises are valid and so it is to expect that a conclusion is valid too. But what about the cases where one of premises is false? Or where both of premises are false but conclusion is valid? Hm. I`m close to start to feel a headache.

If we follow strictly rules of formal logic, an argument is valid if the conclusion follows logically from the premises. For example:


  • All hippopotamuses eat cockroaches. (let`s assume this)
  • Mr Porter is a hippopotamus. (It is possible that some hippo somewhere in the world is called Mr Porter).


  • Therefore Mr Porter eats cockroaches.

Both premises are false and conclusion is true! (but the argument is still valid).

Both premises and conclusion are false, but the argument is valid. The way we argumented Mr Porter`s eating habits is valid.  But the conclusion is true only when both of premises are true.

Let`s consider something else:

  • All ducks are teachers. (obviously, not truth)
  • Mr Porter is a duck. (this might be truth)
  • Therefore Mr Porter is a teacher.

In this case we see that either one or both premises are false but conclusion is valid.

A quick task for students; they write on a piece of paper their examples of syllogisms, where both of premises are valid and where one or both of premises are not valid.

Inductive and deductive reasoning 

The last part of development part of a class is dedicated to an explanation of the difference between inductive and deductive reasoning.

Whilst deductive reasoning goes from the general fact (or an opinion) to the particular, inductive reasoning goes from the particular facts or opinions to the general. Since inductive reasoning goes from the observed to the unobserved (usually present in sciences), it enables us to make generalizations about the world.

  • All metals expand
  • All human beings are mortal

These are examples of generalizations but true generalizations. Sometimes (or very often, to tell the truth) is not enough to create, to say or to write generalization on a basis of one (empirical) example. If we saw a dog once to swim, it is not enough to claim then that all dogs swim.

Thinking out of box

  • Lateral thinking (Eduardo de Bono)


Common fallacies

Here is the list of some common fallacies which students may notify if use reason as way of knowing as one of tools in their research ( when start (or in a process of) to develop their TOK presentations and essays.)

Ad hominem (Latin for “to the man”).

  • An arguer who uses ad hominems attacks the person instead of the argument. 

Appeal to ignorance (argumentum ex silentio)

  • if we have no evidence for something, it must be (or it can be) that something that is spoken about exists. We don`t have evidence that the Universe started at some point but still we claim this is true. The similar can be applied to the question of God`s existence.

Argument from omniscience

  • Someone tries to persuade you in something with use of expressions such as, “All people believe in that”, or ” Everyone do that.”

Appeal to faith

  • You have to believe in that! – says a person who wants to convince you in something. For instance, how can you discuss about God`s existence if you don`t believe in God?

Appeal to tradition

  • Someone tries to convince you in validity of something because he or she finds an argument in something considered as traditional (astrology, religion etc.)

Argument from authority (argumentum ad verecundiam)

  • when someone uses the words of an “expert” or authority as the bases of the argument instead of using the logic or evidence that supports an argument

Argumentum ad bacalum

  • an argument based on an appeal to fear or a threat

Argumentum ad populum

  • Someone wants to convince you in something on the basis of sentimental weakness rather then facts and reasons.


Bandwagon fallacy

  • Something is “true” just because “so many people believe in that”.

Confirmation bias

Someone beliefs in something that he or she prefers to believe in rather then facts and reason.  Selective thinking that focuses on evidence that supports already believe while ignoring evidence that refutes their belief.

Confusion of correlation and causation

  • when someone believe in his or her own reasons for approval of something else “Children who watch TV a lot tend not to learn too much.”

Excluded middle

  • There is no “in between”. Or you believe that something is black or that something is white. There is no grey zone in this story. 

Half truths (suppressed evidence)

  • Someone tries to hide half validity of his or her statement.

Meaningless question

  • Is everything possible? 

Non sequitur (Latin for “does not follow”)

  • A conclusion that does not follow from established premises or evidence, ” Many people tend to fall in love during the fool moon.”. There is no evidence for this.

Observational selection

  • Pointing out favorable circumstances while ignoring the unfavorable.

Slippery slope

  • a change in procedure, law, or action, will result with.. When? A problem appears when someone tries to convince you if A happens ..that even.. Z..might happen once..
  •  (e.g., If we allow doctor assisted suicide, then eventually the government will control how we die.)

Two wrongs make a right

  • trying to justify what we did by accusing someone else of doing the same. (e.g. how can you judge my actions when you do exactly the same thing?)


Closure: 15 minutes

Evaluation of a class


Lindsay, Don, A list of fallacious arguments

Kahneman, David, Thinking fast, thinking slow

Click to access Daniel-Kahneman-Thinking-Fast-and-Slow-.pdf

Kahneman, David, Maps of bounded rationality, A perspective on intuitive judgement and choice

Click to access kahnemann-lecture.pdf



Overview of Examples & Types of Syllogisms


Reason for being


Epistemology, How we gain knowledge, You Tube

Fry, Stephen, Philosophy, Logic, Reason, You Tube

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