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What is the difference between good and bad reasoning?

What we are going to have to come to terms with is that human reasoning is far from perfect.
In order to answer the question about how good our reasoning is, we need some means of distinguishing between good and not so good reasoning. Here we can turn to a simple analogy. Chess is a board game characterised by certain rules. The rules set out how each Chess piece can move on the board. To understand the rules of chess you must commit these allowable moves to memory. So to know how to play chess is to understand the rules of the game. We will simply make the claim that a good chess player is someone who plays according to the rule of the game. A good player is someone who applies the rules of Chess in a valid way.
Pawns move forward – valid Pawns move backwards - invalid In the same way we can ask whether a person acts according to the rules of reasoning and applies them in a valid way. In order to do this we must decide on what the rules of reasoning are. To do this we will simply focus on whether human reasoning is rational. Rational good – irrational bad. We can address this question in many different ways but one main way is to see whether people reason logically. In the same way that there are the rules of Chess there are rules of logic. The rules of logic provide us with the means for deciding whether human reasoning is valid (rational) or invalid (irrational).
We will begin by focussing on the notion of a logical argument. We can characterise a logical argument in the following way We state a claim, provide some evidence and then draw a conclusion. Consider the following • All men are mortal. • Harry is a man. • Therefore Harry is mortal. All men are mortal is our claim Harry is a man is some evidence Therefore Harry is mortal is the conclusion When we examine this line of reasoning we are solely concerned with whether the conclusion follows in valid way from the claim and the evidence. The experts in logic – the logicians – tell us that this kind of argument is logically valid.
So Yes Harry is a mortal does follow from our claim and the evidence. But as cognitive psychologists we can ask lots of questions about how humans deal with these kinds of arguments Do people naturally reason this way? Do people readily accept that the conclusion is valid? The overriding question is do humans reason logically. In brief the answer is sometimes. This conclusion is supported by lots of experiments on how humans reason when confronted by claims and evidence. We intend to engage you in some of the experiments as the course unfolds.

Some concrete examples

Let’s take a claim:
If there is a cat on the mat then there is a fish in the fish bowl.
Let’s also take the evidence:
There is a cat on the mat.
Consider the conclusion:
There is a fish in the fish bowl
And what the data show is that most people readily agree that the conclusion is valid.
It’s the same kind of logical reasoning that underpins the Harry example discussed by Rob in the video.
However, let’s take the same claim:
If there is a cat on the mat then there is a fish in the fish bowl.
And take some different evidence:
There is not a fish in the fish bowl.
Now consider the following conclusion:
There is no cat on the mat.
This time the data show that some people struggle to see that this conclusion is valid.
Human reasoning therefore can appear a little quirky.
Some valid arguments are readily understood others are not.

Time for you get thinking

As the material this week unfolds you must bear in mind several things. First unless you are genius, a real genius, then you will tend to be tripped up by some of the puzzles we present. However, if you do manage to reason logically about everything we present then that will be exceptional. It is, therefore, best to be prepared for the fact that, in some cases, you will be shown to reason irrationally. This is not exceptional – sometimes a few people err, and sometimes most people err.
What we as cognitive psychologists are trying to do is understand how and why people make errors in their reasoning. If we can understand this then we can take steps to try and help them avoid similar errors in future.
Ok let’s get started…
Here’s a claim:
If it’s raining, I get wet.
Now some evidence:
I get wet.
Is it therefore valid to conclude that:
It’s raining??


The answer is provided in the next step so before moving on work out what you conclude.
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Introduction to Cognitive Psychology: An Experimental Science

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