A picture of two birds arguing.

How Arguments Work: The Basics

If you understand how arguments succeed and fail, then you can do some important stuff. You can construct a convincing argument, evaluate an argument, fix a broken argument, and — maybe most importantly — avoid being duped by a bullshit argument. So if any of that sounds interesting to you, then you’ll want to understand the basics of how arguments work. I’ll review those basics in the rest of this post. 1  How good arguments work

Arguments are supposed to fulfill a couple conditions. The conditions are pretty intuitive, but just to make sure that we’re on the same page, we’ll review this summary:

Arguments consist of truth-bearing [premises] called propositions. A proposition is any meaningful utterance that can be true or false, like ‘over 90% of climate scientists believe in anthropogenic climate change’ (true), ‘New York City is the capital of New York state’ (false), or ‘it will rain tomorrow’ (unknowable today). […] Propositions can be combined in ways such that their truth content gives us information about the truth content of other propositions. If some set of propositions being true (the premises) makes some other proposition (the conclusion) more likely to be true, then we can say that the truth of the premises supports the truth of the conclusion. The degree of this support provides us with an important criterion for the judging the quality of an argument. If the truth of an argument’s premises have no bearing on the truth of its conclusion, we say that the argument is a non sequitur. (Cook, Ellerton, and Kinkead 2018, 2)

1.1  Two Qualities of Good Arguments

According to these basics, our argument’s premises are supposed to…

  1. Be true — or at least plausible. (Philosophers call this ‘soundness’).
  2. Support their conclusion. (Philosophers call this ‘validity’).

1.2  Two Kinds of Argument

There are at least two ways for our premises to support our conclusion. First, our premises can support our conclusion by making it necessarily true. (Philosophers call this deduction). Second, our premises can support our conclusion by merely making the more probably true. (Philosophers call this induction).

2  Four Bad (But Common) Argument Forms

So good arguments have both true premises and premises which support their conclusion. This means that bad arguments will lack one or both of those qualities. Let’s check out four common forms of a bad argument that we might otherwise mistake for a good argument.

2.1  True Premises That Don’t Support Their Conclusion

Premise 1: Cats tend to have four legs.
Premise 2: Dogs tend to have four legs.
Conclusion: Cats are dogs.

We can see that the premises are true. Alas, we should notice that these premises do not support the conclusion. After all, the two premises can be true without the conclusion being true.

2.2  False Premises That Do Support Their Conclusion

Premise 1: A country’s capital is its most populous city.
Premise 2: New York City is the United States’ most populous city.
Conclusion: The capital of the United States is New York City.

We can see that these premises support the conclusion. That is, if we think that the premises are true, then we have to think that the conclusion is true.

But maybe you noticed that the first premise of this argument is false. So the conclusion is not necessarily true. And that makes sense, given that the conclusion is, in fact, false.

2.3  False Premises That Don’t Support Their Conclusion

Premise 1: The news is biased.
Premise 2: If something is biased, then it is wrong. 
Conclusion
: The president is innocent.

Maybe you notice that this argument has both problems. First, one of the premises is false — bias does not entail falsehood. And second, the premises do not support the conclusion. The most obvious way for you to notice that premises do not support their conclusion is to see if the conclusion contains stuff that is not mentioned in the premises. In this case, our premises make no claims about the president or innocence. So our premises do not allow us to conclude anything about the president or innocence.

2.4  A bad argument for a true conclusion

We are more prone to accept a bad argument if we think that its conclusion is true. This is called belief bias (Markovits & Nantel 1989). If you want to overcome this bias, then try to memorize this: true conclusions don’t make their arguments good. Let’s take a look at an example:

Premise 1: If someone is unemployed, then they are poor.
Premise 2: Oprah is not unemployed. 
Conclusion
: Oprah is not poor.

We might unreflectively think that this is a good argument. After all, the conclusion seems true. So the argument works, right? Not quite. The premises do not actually support the conclusion (because the premises commit the fallacy of denying the antecedent). So even though the conclusion of the argument is right, the argument is wrong.

3  Test

Now let’s put your new knowledge of the basics to the test! Consider two similar arguments. And ask yourself, “Which of these arguments, if any, work?”

Premise 1: All Xs are Ys.
Premise 2: Z is an X.
Conclusion: Z is a Y.
Premise 1: All Xs are Ys.
Premise 2: Z is a Y.
Conclusion: Z is an X.

I’ll give you a hint: one of these arguments fails.

Ok. I’ll just tell you: It’s the one on the right. Why? Because the conclusion on the right isn’t supported by its premises.

Try Again

In case that last test wasn’t obvious, let’s replace the Xs, Ys, and Zs with ordinary stuff.

Premise 1: All pregnant humans are female.
Premise 2: Zoe is a pregnant human.
Conclusion: Zoe is female.
Premise 1: All pregnant humans are female.
Premise 2: Zoe is a female.
Conclusion: Zoe is a pregnant human.

Obviously, one can be a female without being pregnant — even if premise 1 is true: all pregnant humans are female.

Take-aways

There are two points here.  First, the difference between good and bad arguments can seem subtle at first. Second, you might get a better sense of how arguments work by substituting familiar objects for whatever you find in the original arguments. (That only works if you maintain the form of the argument, of course.)

4  Recap

Those are the basics. Let’s review:

  • Arguments’ premises are supposed to be true (or plausible).
  • Arguments’ premises are supposed to support their conclusion.
  • Good arguments can support false conclusions.
  • True conclusions do not make their arguments good.
  • The difference between good and bad arguments can seem subtle.
  • If it’s not obvious how an argument works, try making the argument about something familiar.

These principles might be easy for us to remember. But it is hard for us to apply the principles when presented with new arguments. So — as always — we will want to practice. One place to start practicing is this post.

Published by

Nick Byrd

Nick is a cognitive scientist at Florida State University studying reasoning, wellbeing, and willpower. Check out his blog at byrdnick.com/blog

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