Critical Thinking with Argument Maps

By Dave Kinkead, University of Queensland Critical Thinking Project

The truth, the whole true, and nothing but the truth

We’ve seen now that we can use arguments to establish the truth of some claim, based on the truth of some other claim. But what do we mean here by truth and where does this truth come from?

That’s actually a very deep philosophical question and one that we can’t hope to answer fully here but it’s easy enough to categorise truths based on what makes them true.

So very quickly, a claim can be true because we made it true, we saw it true, we were told it was true, or we reasoned it true.

Making truth

The simplest way to make something true is to define it as true.

What makes it true that 1 + 1 = 2? A mathematician posited it so. What makes it true that a bachelor is an unmarried man? A dictionary defined it so. What makes it true that I’m married? A celebrant proclaimed it so.

Truth of this type is created. Which means if the buses are consistently running late to uni, then Brisbane City Council can just redefine the meaning of late and the problem is solved!

Ok, not so fast – this type of axiomatic truth can only extend to the meaning of things. So while we can define the meaning of the term “a rainy day” to mean a only day with more that 20mm rain, we can’t define our way to knowing whether or not 20mm of rain actually fell.

Seeing truth

Another way of knowing truth is by touching, seeing, hearing, or otherwise perceiving it. We call knowledge derived from observation like this empiric. Surveys, personal experience, experimental and statistical results are all examples of empirical claims.

Importantly, empirical claims are verifiable. I can verify someone’s claim that it’s raining by looking out the window, and scientists can verify the claims of others be repeating the experiment. This gives us very strong grounds for believing these types of claims as true (assuming we can verify them).

Accepting truth

Often however, we don’t have direct access to experience or data ourselves. In these cases, we need to rely on the expertise and testimony of others to know what is true or false.

Did you see the bombing of Pearl Harbor yourself? Then how do you know it really happened? Did you view the tissue samples of your last biopsy yourself? Then how do you know the test was negative?

The vast majority of our beliefs are based entirely on the word of other people. As such, it behooves us to make sure we have good reasons (and systems) for believing them.

Deriving truth

Finally, we can determine which claims are true or not by reasoning or inferring our way to the truth.

This is where we can use argumentation (and argument mapping). If we know that some claims are true, this can tell us whether other claims are more likely to be true or false.

Argument maps depict inferential connections – they show how the truth of the conclusion is derived from the truth of the premises. If there are arrows between claims, then that arrow represents an inference.

Everything else requires evidence. If a claim doesn’t have an arrow pointing to it, then you need to be able to show evidence of it being true.

So let’s look at your first in-no-way-controversial argument like abortion or homosexuality. It might have looked something like this …

The arrows from the premises to the conclusion indicate that we are reasoning our way to the truth (or falsity) of the conclusion. But how do we know the premises are true?

Take a moment to think about what would be appropriate evidence for those two claims. Are they axioms? Can we know them from empiric observation? Do we need to rely on the testimony, expertise, or authority of others to know they are true?

In my example, I could rely on an axiom like “all reasonable people believe murder is wrong”, or some authoritative source.

Next lesson …

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