Critical Thinking with Argument Maps

By Dave Kinkead, University of Queensland Critical Thinking Project

You’re not entitled to your opinion

Everyone has an opinion about something and we’ve already seen how we can express our beliefs on what is true (or not true) about the world in propositional form.

“Today is Monday” … “Pineapple on a pizza is a crime against humanity” … “The Queensland Reds are going to win the super rugby grand final” … you get the idea.

Statements like these are called assertions because we assert that the claims are true.

But not everybody holds the same beliefs that we do. Some people have different values, some people make reasoning errors, and some people are confused or just plain wrong.

So merely asserting things isn’t good enough. If you want other people to believe as true the things you believe are true, you need to offer them reasons for believing. And these reasons need to be ones that they will accept.

So to justify our beliefs, we also need to state why we believe them to be true. For example …

“Today is Monday because it’s Jan 20, 2020 and my calendar says that that day is a Monday”

“Pizza is the sublime expression of humanity’s finest culinary achievement. Putting pineapple on it would be a form of cultural vandalism akin to using the Mona Lisa as a cleaning rag.”

“The Queensland Reds have been playing brilliantly since …. “ Ok. Not all our beliefs can be justified.


To give reasons for our beliefs is to offer an argument. Arguments don’t always mean conflict. In an academic context, an argument is a connected series of statements used to establish some conclusion.

We use arguments to establish the truth of some claim by appealing to the truth of other claims. We call the claim that we trying to establish as true the conclusion. We call the other claims the premises.

It’s important that the premises are claims we already accept as true. If the premises are true, and the argument is a strong one, then we have very good reasons for believing that the conclusion is true. We can say that it is justified.

Note here the direction of the arrow. The justification flows from premise to conclusion – this is what distinguishes an argument from an explanation.

So with that in mind, let’s move beyond mapping opinion and assertions – let’s add a justification.

On your previous map, click the fork button to create a new copy of your map.

Now, double click the blank canvas to add a new propositional claim as a justification to your previous assertion.

Then drag your justification onto the original claim to indicate what it is justifying.

If you make a mistake, just select the claim or connection and press delete.

For my map, I’m going to try and justify the claim that “abortion is wrong”. Not because I believe it but because reasoning about claims in which you hold strong prior beliefs is a very useful way to teach critical thinking.

Did your map look like this? Excellent – you now have an argument on your argument map!

Next lesson …

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