IB TOK: What is deductive reasoning?

This is the Monty Python ‘witch scene’ from ‘The Holy Grail’– an entertaining clip where you can spot the multiple flaws in reasoning!

Deductive reasoning starts with premises and argues to a conclusion. Here are two examples of syllogisms which contain two premises and a conclusion:


Premise 1: Typically men earn more money than women.

Premise 2:  I am a man.

Conclusion: Therefore I earn a lot of money.


Premise 1: I am an IB student.

Premise 2: All IB students suffer from an unbearably large workload.

Conclusion: Therefore I must suffer from an unbearably large workload.


The arguments move from a general claim in premise 1 to a particular conclusion. In order for the conclusion to be true, both premises must be true and the argument must be valid. In the final example about IB students, you might consider the truth of premise 2 (few would dispute this!) and whether the argument valid?

You may want to invent your own syllogisms based on your IB subjects to try out different variations of true and untrue premises and valid and invalid arguments.

When you think about syllogisms consider:

1.      Are both premises either true or not true?

2.      Is the argument valid or invalid?


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1 Response

  1. This is a really good tip especially to those new to
    the blogosphere. Simple but very precise information… Thanks for sharing this one.
    A must read article!

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