Critical Thinking Fallacies Of Relevance Chart

As we saw in the previous lesson, valid arguments contain premises that lead to

a conclusion in a formal logical structure.

For example, a formal logical structure could look like of it's 5 PM,

then I can leave work.

It's 5 PM.

Therefore, I can leave work, but what happens if the logical structure is

correct, but you have one or more flawed premises?

In this lesson, we'll be looking specifically at logical fallacies

related to premises and how these weaken an argument.

Let's start with the fallacy of jumping from correlation to cause.

This fallacy occurs when you can see two phenomena are related and

you conclude that one phenomenon causes the other.

For example, in this graph, we see a strong positive correlation between

sales in ice cream and shark attack incidents.

This claim possibly arises from an argument that follows a formal logical

structures such as.

Two trends that occur at the same time exist in a cause-effect relationship.

The trends of increased shark attacks and

increased ice cream sales occur at the same time.

Therefore, shark attacks are caused by increased ice cream sales or vice versa.

You might find this argument convincing at first,

because it follows the structure of formal logic.

However, even if the structure of an argument is logical,

we need to check that all the premises are sound.

You might have identified that the first premise was problematic.

We can't assume correlation implies causation.

It might be the case that the two trends are completely coincidental or there

might be an unexamined third factor, which is causing both trends independently.

For example, the onset of warmer weather could be the cause of increased shark

attacks as more people swim in the open at that time.

Warmer weather could also explain an increase in ice cream sales.

To recap, although the logical structure of the argument is valid premises

that directly infer causation from correlation are a logical fallacy and

you should watch out for these in your own arguments and in the arguments of others.

Let's look at two more fallacies involving faulty premises.

The next one is called hasty generalization.

A hasty generalization draws a conclusion

about a class based on too few or atypical examples.

Generalizations are arguments that make a general comment based on specific


Unwarranted generalizations are called stereotypes.

For example, homeless people live on the street or

homeless men are middle-aged men.

These claims that homeless people live on the street and

homeless people are middle-aged men might be based on someone's

own limited observations or experiences of homeless people,

which have been extended to a comment about all homeless people.

Generalizations that are personal or anecdotal, or based on a small sample

size are problematic and should not be used as evidence for an academic argument.

We can see this when we test the validity of these claims.

For the first claim about homeless people living on the street, census data

reveals this proportion of homeless people is actually in the minority.

According to the Australian Bureau of Statistics,

there are actually only 6% of homeless people that sleep in the street.

In addition to the policies of jumping from correlation to cause and

hasty generalization, you should also be wary of the straw man fallacy.

Let suppose that someone has made this argument, a solution to the problem of

homelessness in Australia requires investment in affordable housing and

someone else has counter-argued giving homeless people free

houses may encourage more people to become homeless.

A counterargument contains a straw man fallacy,

if it misrepresents the original argument.

In the previous example, this occurred when the argument for investment in

affordable housing, we substituted for giving homeless people free houses.

At university, when you're asked to respond to someone else's position,

make sure that you represent their position accurately, so

your counter-argument is relevant.

If you quote someone out of context or simply oversimplify their

argument in order to weaken it, you are committing the straw man fallacy.

You will find the straw man fallacy is often committed in academic context,

even by academics who should know better.

So in this lesson, we've looked at three common logical fallacies that we can any

argument or counter-argument.

There are many more fallacies that can occur,

some of which are more common than others.

A quick look online will introduce you to these if you’d like to find out more.

At university, you can apply your knowledge of logical fallacies in order to

strengthen arguments in your own essays and presentations by avoiding logical

fallacies and evaluate the arguments of others by identifying flaws in reasoning.

This is one way to demonstrate critical thinking.

And finally, here are two further tips to keep in mind.

Since there are different names for

logical fallacies and not everyone is familiar with them, you should summarize

the flaw in reasoning that you've found rather than using terms such a straw man.

Secondly, keep in mind that an argument may still be true

even if it commits a logical fallacy.

Otherwise, you commit the fallacy fallacy and disregard conclusions that are true,

simply because they were drawn from a weak argument.


A logical fallacy is a flaw in reasoning. Logical fallacies are like tricks or illusions of thought, and they're often very sneakily used by politicians and the media to fool people. Don't be fooled! This website has been designed to help you identify and call out dodgy logic wherever it may raise its ugly, incoherent head. Rollover the icons above and click for examples. If you see someone committing a fallacy, link them to it e.g.

  • Critical Thinking Cards

    Get a deck of 54 fallacies and biases cards for honing critical thinking skills, calling out people you’re arguing with, or spotting actual fake news. Also available as a Creative Commons pdf download.

    Click here to check it out

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You might be interested in a new book on mental models

Co-authored by Gabriel Weinberg who is the CEO of DuckDuckGo and an advisor to The School of Thought.

You can see a brilliant Medium post he wrote on this subject here.

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