What makes an argument valid?

Have you ever been in a situation where a
person makes an argument, and it goes, “Premise, premise, premise, therefore conclusion,”
and you think, “I agree with your premises, but your conclusion just doesn’t follow.” Or maybe you think the inference is good,
but the premises are way off base. Maybe you actually agree with the person’s
conclusion, but think this is a lousy argument for it. What you’re noticing is that there are different
ways an argument can go wrong—and the good news is: Philosophy can help sort those out. Here I want to talk about a philosophical
concept called validity. An argument is valid when it’s structured
in such a way that if the premises are true, the conclusion must be true as well. It’s a truth preserving structure. Now, in everyday language people will sometimes
use the term “valid” much more loosely. They’ll say, “That’s a valid point!”
to indicate agreeement. In philosophy, we use it more specifically. Again, it’s about good argument structure. Take a simple example. This argument: If my office is in Detroit, then my office
is in Michigan. My office is in Detroit. Therefore, my office is in Michigan. Now, it happens to be the case that those
premises are true: My office is in Detroit, and if an office is in Detroit then it’s
in Michigan. Apologies to the folks in Detroit, Tennessee. But whether or not those premises are true
that argument is valid. Why? Because if those premises are true, the conclusion
has to be true as well. And again, validity is about the structure,
not the content of arguments. Take another example: If my office is in Paris, my office is in
Michigan. My office is in Paris. Therefore, my office is in Michigan. Is that one valid? Now you might be thinking, “Your office
isn’t in Paris!” Are you sure? It doesn’t matter. The argument is still valid. Because the structure is such that if those
premises were true—which they’re not—the conclusion would have to be true as well. In fact, this has the same structure as the
previous argument. The structure is: If P then Q; P; therefore
Q. We can worry later about whether the premises
are true. Once you know that that’s a valid argument
structure, it’s valid no matter whatever you plug into that, as long as you’re consistent
with your P’s and Q’s. A valid argument can have true premises and
a true conclusion, false premises and a false conclusion, false premises and a true conclusion. But not true premises and a false conclusion. Why not? Because—I’ll say it again—the definition
of a valid argument is one where if the premises are true, the conclusion must be true as well. Now you might be thinking, this validity thing
doesn’t sound very impressive. I mean, you can still end up with a false
conclusion. Well that’s right. Argument structure is only half the battle. You also have to pay attention to content:
You want true premises. The term we use for a valid argument with
only true premises is a sound argument. A sound argument proceeds from true premises,
to a true conclusion that follows. Causing peace and prosperity to reign across
the- okay, not really. But, in deductive arguments, soundness is
what you want. Which brings me to my final point, which is
that validity is about deductive arguments; arguments where the premises are meant to
guarantee the conclusion. There are also inductive arguments, where
the premises are meant to show that the conclusion is likely or probable. Now those are trickier—but even there, you
should pay attention to the difference between structure and content. I’m John Corvino, and this is Better Argument.

3 Replies to “What makes an argument valid?”

  1. Great videos. But I think you should space them out more. Upload for example once or twice every week. Keeps your audience more engaged than suddenly uploading ten videos and then being silent for a while. Plus the YouTube algorithm rewards it.

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