Critical Thinking and Civil Debate for Ordinary Life (and Ethics, btw)

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This lesson is about how basic critical thinking works, and how important it is when discussing issues that are controversial or personal or are otherwise disposed to unnecessarily heated discussions. I will begin by showing that techniques exist for this, both for regulating emotions and then for proceeding in a rational way regardless of how you feel.

The first activity is that students watch the following TEDed video with prominent Harvard political philosopher Michael Sandel:

Below is a guide to most of the common fallacies. A fallacy is a mistake made in an argument, a “bad move” in the game of civil discussion. Students should read this very carefully before moving on.

Here's a simple guide to all the falacies


Of course, knowing that there’s a mistake out there for a discussion, and that it has the fancy name of “fallacy” doesn’t get us all the way to how to construct an argument. For that, we’re going to need just a little more instruction. That’s what I’ve provided next, an expanded discussion of what an argument is and what makes one good.


Arguments are made of two parts, premises and conclusions.

Premises are independent statements that are supposed to support the conclusion.

Conclusions are dependent statements that are evaluated on the basis of how well supported by the premises.



The next concept is the trickiest one, the idea of what it means for premises to support their argument well.

This relation, the relation of the premises supporting an argument well, is called Validity.

What confuses people about validity is that it’s just a formal notion about coherence between the premises and the conclusion, and not the notion they really want Truth.

Truth is a separate animal, concerning whether a statement (in this case, the conclusion of the argument) really is the case (whatever that means).

So, we want truth about our arguments, but most of the time, we can only evaluate an argument on whether it’s valid. It often takes a lot of experience or independent study to determine (imperfectly) if a claim is true at all.

When a conclusion is valid, we say so, and call the argument “valid”. If a valid conclusion of an argument goes the extra mile and also turns out to be the way things really are, we go and say the conclusion is true” and the argument is Sound.


Here’s an example of an argument that is invalid:

1. Tallahassee is the capital of Florida.

2. Washington D.C. is the capital of the United States.

C: Rick Scott is the governor of Florida.

This will seem wrong, but in a politically-correct and common-sense way (which, in this case, is the wrong way). It’s not enough that it “sounds wrong” to you, because that assumes you’re right rather than proving it. So what’s actually wrong with it. Well, though the premises do follow from the conclusion if understood loosely, it’s pretty clear that premises aren’t clearly related to each other, or the conclusion. Two statements about capitals lead to a conclusion about a governor. It’s true that a governor is someone who lives in a state capital, but notice that the order and content of the statements, as indicated, doesn’t justify making a consistent statement about where a governor lives. Instead, we just have three true but only loosely-related statements, which don’t succeed at even adding up to an argument because the premises don’t instantiate the relationship of validity as they culminate in their conclusion.

Here is an is valid but not sound:

1. Colorless green ideas dream furiously.

2. Bob is a colorless green idea.

C: Bob dreams furiously

So, this just has to be wrong, right? It doesn’t even make sense. Well, literally, no, it doesn’t. But, if you accept the premises “for the sake of argument” (thus, finally showing that that phrase means) you’ll see the lead right to the conclusion. So, while we don’t know what it means for a “colorless” green idea to do something like dream, much less dream furiously, we know that that the conclusion is logically consistent with the nonsensical premises. We are still justified in holding of any X that if X is a colorless green idea, then X dreams furiously, and that’s just what this argument  says. So it’s valid, but the utter nonsense of the contents (caused by using inappropriate grammatical categories and inappropriate verbs) prevents us from ever being able to tell whether that what’s really the case, so we can never say whether it’s true.

Here is an example of an argument that is sound:

1. All men are moral

2. Socrates is a man

C: Socrates is moral

This one is, literally, one of the oldest examples in the book, going back to Aristotle. However, consider the fact that if you grant premsies 1 and 2, for the sake of argument, it would be impossible to deny the conclusion. Thus the argument is valid. Furthermore, since Socrate is (or at least was) mortal, it appears to be true as well. Thus we can be sure this is a sound argument, the gold standard of arguments.


So now you know what a fallacy really is, it’s a systematic failure of validity in an argument. Sometimes, fallacies don’t guarantee the argument is wrong but are just generally bad ways to interpret some premises as supporting a conclusion. Either way, it’s a bad way to argue.

Writing prompt:

What fallacies are most common when people engage in heated discussions? Are these the only fallacies people have to worry about? Give an example of where a fallacious argument, combined with a poor response, resulted in discussion of a sensitive topic getting out of hand.


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