What is the difference between reason and logic? How reliable is inductive reasoning? Are we predictably irrational?

Bear in mind, of course, that no WOK is an island and all interact with each other to produce this thing we call ‘knowledge’.

We are going to be looking at what we mean by reason. Is reasonable behaviour the same as acting with reason, or acting with a reason? We need to be clear, when discussing reason, exactly what we mean. We are going to be considering the relationship between reason and emotion, the extent to which we can trust knowledge arrived at through reasoning and the sorts of nonsense we can arrive at through weak or fallacious reasoning.

Let’s begin with a ‘test’ of your ability to think logically.


What does your result tell you? Is there anything wrong with the test? What might its limitations be?

1. Logic and formal reasoning

In logic, a syllogism is a form of deductive reasoning consisting of a major premise, a minor premise, and a conclusion.

There are three broad types of syllogism:

i) Conditional syllogisms are better known as hypothetical syllogisms, because the arguments used here are not always valid. The basic structure of this syllogism type is: if A is true then B is true as well.

a] If you don’t study hard you won’t succeed in life

b] Simone doesn’t study hard

Conclusion: Simone won’t be successful in life

Of course, we can see that premise [a] is not necessarily true. It is possible to not study hard and to be successful. In common speech, we often omit one of the premises in these types of syllogism, such as ‘Mandy wasn’t in school today so she must be at home’ (The missing premise being, if she’s not at school, she’s at home.)

ii) Disjunctive syllogisms do not actually state that a certain premise (major or minor) is correct, but is does states that one of the premises is correct. The basic type for this syllogism is: Either A or B is true, but they can’t be true at the same time. Example:

a] The game is either in Nanjing or in Shanghai

b] The game is not in Shanghai

Conclusion: The game is in Nanjing.

iii) The third and most commonly used type of syllogisms are the categorical syllogisms. The basic for this syllogism type is: if A is a part of C, then B is a part of C (A and B are members of C). An example of this syllogism type will clarify the above:

a] All humans breath air

b] Bill is human

Therefore: Bill breathes air.

BUT, beware! The argument can be valid, but untrue. for example:

Every human likes to eat fish.
I am human
Conclusion: I like to eat fish.

Here, one of the premises is wrong, so despite this being a valid argument from the point of view of logic, it gives a false conclusion.

You can have any of the following situations:

  • Two true premises and a true conclusion.
  • One true premise, one false premise and a true conclusion
  • One true premise, one false premise and a false conclusion
  • Two false premises and a true conclusion
  • Two false premises and a false conclusion

Take a moment to come up with an example of each. Note that you CANNOT have two true premises which give a false conclusion – at least I have been unable to come up with an example!


Follow this link to try some out.

2. Creativity, deduction/induction and analogy

In Creative Thinking, we are thinking outside the box. Sometimes lateral thinking is the term used. Programmes such as Edward De Bono’s Six Hats are examples of how this process works.

Consider these:

i. You are driving down the road in your car on a wild, stormy night, when you pass by a bus stop and you see three people waiting for the bus

  • An old lady who looks as if she is about to die.
  • An old friend who once saved your life.
  • The perfect partner you have been dreaming about.

Knowing that there can only be one passenger in your car, whom would you choose?

ii. Acting on an anonymous phone call, the police raid a house to arrest a suspected murderer. They don’t know what he looks like but they know his name is John and that he is inside the house. The police bust in on a carpenter, a lorry driver, a mechanic and a fireman all playing poker. Without hesitation or communication of any kind, they immediately arrest the fireman. How do they know they’ve got their man?

iii. How could a baby fall out of a twenty-story building onto the ground and live?

iv. There are six eggs in the basket. Six people each take one of the eggs. How can it be that one egg is left in the basket?

You can find these and many other examples on lateral thinking sites in the internet.

Deductive Reasoning involves working from broad generalisation to arrive at specific conclusions. Sound familiar? Yes, it’s those syllogisms again.

Inductive reasoning is about observation and generalisation. It is essentially the scientific method. A scientist has come up with a hypothesis (a general statement – deduction) Her next step is to see if her idea is any good.  This involves testing her hypothesis by carrying out experiments. If the experiment works, her hypothesis is strengthened, and she will go on to do more demanding or  extensive experiments. If it doesn’t work, then she has to go back to the drawing board and start again. Observing specific events leads to generalised rules or conclusions.

Deductive Reasoning Versus Inductive Reasoning

In analogical reasoning we use logic and analogy. There are two steps to analogical reasoning:

  • Recognizing that two or more things have something in common
  • Assuming that if they have one thing or characteristic in common, they will also have others in common

This can take the form of studying past exam papers, working on the assumption that future examinations will be similar, or taking a particular medicine for a symptom which is similar to a symptom that the same medicine worked for previously. We use both deductive reasoning (going from general rules and making an assumption about a specific case) and inductive reasoning (going from observable specifics to generate or validate general rules)

3. Logical Fallacies

Look through this Keynote presentation – it’s very wordy but you don’t need to memorise it. Then look through some popular news or gossip websites and see if you can spot any examples. Make a journal entry explaining how each of your (three or four) examples is a logical fallacy.

TOK – Logical fallacies

Fallacy Detective Lessons


Over to you…

Now, using all your new-found thinking skills and reasoning abilities,
can you solve this problem? The question you need to answer is ‘How does she know?’

Follow the link below and choose two of the reason-related Knowledge Issues to consider. Think about them, try to link them to your own experiences, and make a journal entry of about 200 words for each one.

Reason knowledge issues and links with other WOKs and AOKs


How rational are you? Read this article about SUPERSTITION and take the test at the end. How do you feel about the score you get?

One thought on “Reason

  1. Hi,

    I have been doing independent ( out of my natural curiosity to know) research, contemplation and studies on man’s faculty of reason for over 2-3 decades. I observe that while we use word ‘reason’ frequently in day to day life situations, in science,and philosophical pages like this one, it is without first declaring what ‘reason’ as such is ! I recently read a philosophic paper that says, though Kant had elaborately touched on the reach and limits of reason, he too missed to touch the central question of what reason as such is.

    I have attempted to find out answer to this important question, and its findings are there at two sources;
    1) at my Amazon, with link:
    2) At my blog:

    Being the owner of this page seems an expert on the subject of reason and Logic, I am keen to share my findings with him, and seek his comments !

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