3. What is a Good Argument?

An argument is an attempt to persuade, but the goal of logic and argumentation isn't simply to persuade — it's to persuade for good reasons.

The most basic definition of a good argument is straightforward: it's an argument that gives us good reasons to believe the conclusion.

There's not much we can do with this definition, though. It's too vague. We have to say more about what we mean by "good reasons" obviously.

To do this we'll start by looking at some ways that arguments can fail to be good, and from these we'll extract a couple of necessary conditions for an argument to be good.

Here's an argument:

1. All actors are robots.
2. Tom Cruise is an actor.
Therefore, Tom Cruise is a robot.

Here's another argument:

1. All tigers are mammals.
2. Tony is a mammal.
Therefore, Tony is a tiger.

Both of these are bad arguments, as you might be able to see. But they're bad in different ways.

In the first argument on top, the problem is obviously that the first premise is false — all actors are not robots. But that's the only problem with this argument.

In particular, the logic of this argument is perfectly good. When I say that the logic is good what I mean is that the premises logically support or imply the conclusion, or that the conclusion follows from the premises.

In this case it's clear that if the premises of this argument were all true then the conclusion would have to be true, right? If all actors were robots, and if Tom Cruise is an actor, then it would follow that Tom Cruise would have to be a robot. The conclusion does follow from these premises.

Now let's look at the other argument:

1. All tigers are mammals.
2. Tony is a mammal.
Therefore, Tony is a tiger.

First question: Are all the premises true?

Are all tigers mammals? Yes they are. Is Tony a mammal? Well in this case we have no reason to question the premise so we can stipulate that it's true. So in this argument all the premises are true.

Now what about the logic?

This is where we have a problem. Just because all tigers are mammals and Tony is a mammal, it doesn't follow that Tony has to be a tiger. Tony could be a dog or a cat or a mouse. So even if we grant that all the premises are true, those premises don't give us good reason to accept that conclusion.

So this argument has the opposite problem of the first argument. The first argument has good logic but a false premise. This argument has all true premises but bad logic. They're both bad arguments but they're bad in different ways. And these two distinct ways of being bad give us a pair of conditions that an argument must satisfy if it's going to be good.

First condition:

If an argument is good then all the premises must be true.

We'll call this the "Truth Condition".

Second condition:

If an argument is good then the conclusion must follow from the premises.

We'll call this the "Logic Condition".

Note that at the top I called these "necessary conditions". What this means is that any good argument has to satisfy these conditions. If an argument is good then it satisfies both the Truth Condition and the Logic Condition.

But I'm not saying that they're "sufficient" conditions. By that I mean that they don't by themselves guarantee that an argument is going to be good. An argument can satisfy both conditions but still fail to be good for other reasons.

Still, these are the two most important conditions to be thinking about when you're doing argument analysis.

In later lectures we'll look more closely at both the Truth Condition and the Logic Condition, and we'll also look at ways in which an argument can satisfy both conditions and still fail to be good.

Questions and Comments

1. What’s the difference between “persuading” and “persuading for good reasons”?

If my only goal is to persuade you to accept my conclusion, then I might use all kinds of rhetorical tricks to achieve that goal. I might choose to outright lie to you. If mere persuasion is the ultimate goal then there would be no normative distinction between argumentation and using lies, rhetorical tricks and psychological manipulation to persuade.

Mere persuasion is NOT the ultimate goal of argumentation, at least as this term is used in philosophy and rhetoric. Argumentation is about persuasion for good reasons. Precisely what this means is not obvious, and it will take us some time to work it out work, but at a minimum it involves offering premises that your audience is willing to accept, and demonstrating how the conclusion follows logically from those premises.

Here’s another way to think about argumentation. From a broader perspective, to argue with a person, as opposed to merely trying to persuade or influence a person, is to treat that person as a rational agent capable of acting from, and being moved by, reasons. It’s part of what it means to treat a person as an “end” in themselves, rather than as a mere means to some other end.

In this respect, theories of argumentation are normative theories of how we ought to reason, if we’re treating our audience as rational agents. They’re a component of a basic moral stance that we adopt toward beings who we recognize as capable of rational thought.

2. How can an argument satisfy both the Truth Condition and the Logic Condition and still fail to be good?

I said I would consider this question in a later lecture, but just to give an example, arguments that commit the fallacy of “begging the question” may satisfy both these conditions but fail to be good.

Consider this argument:

1. Capital punishment involves the killing of a person by the state as punishment for a crime.
2. It is morally unjustified for the state to take the life of a person as punishment for a crime.
Therefore, capital punishment is morally unjustified.

Let’s grant that the conclusion follows from the premises. Could this count as a good argument?

The problem is that the second premise simply asserts what is precisely at issue in the debate over capital punishment. It “begs the question” about the ethics of capital punishment by assuming as a premise that it’s wrong. Such arguments are also called “circular”, for obvious reasons — the conclusion simply restates what is already asserted in the premises.

The problem with this kind of argument isn’t that the premises are obviously false. The problem is that they don’t provide any independent reasons for accepting that conclusion.

Logic and critical thinking texts will treat this kind of argument as fallacious, a bad argument. What makes this argument bad isn’t captured by violating the Truth Condition or the Logic Condition.

Arguments that beg the question in this way may well have all true premises and good logic, but they would still be judged as bad arguments due to their circularity.

So this is an example of how an argument may be judged bad even though it satisfied both the Truth Condition and the Logic Condition. And this is what it means to say that these are merely necessary conditions for a good argument, not sufficient conditions. All good arguments will satisfy these two conditions, but not all arguments that satisfy these two conditions will be good.

Still, the distinctions captured by the Truth Condition and the Logic Condition are absolutely central to argument analysis.

3. You keep using arguments with only two premises. Do all arguments only have two premises?

I can see how people might initially get this impression, since so many of the introductory examples you see in logic and critical thinking texts are short two-premise arguments. For the purpose of introducing new logical concepts, the short two-premise argument forms are very useful.

But you can have arguments with five, ten or a hundred premises. In longer and more complex arguments what you usually see are nested sets of sub-arguments where each sub-argument has relatively few premises, but the overarching argument (when you expand it all out) might be very long.

You see this kind of progression learning almost any complex skill. You start out by rehearsing the most elementary concepts or skill elements (basic programming statements in computer languages; the positions and moves of the chess pieces in chess, forehand and backhand strokes in tennis; basic statement types and argument forms in logic, etc.), and then combine them to create more complex structures or perform more complex tasks. Learning logic and argument analysis isn’t any different.