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Evaluating an Argument
Introduction to Philosophy and Ethics
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2 Tutorials that teach Evaluating an Argument

Evaluating an Argument

Author: Glenn Kuehn
Description:

Recognize what makes an argument sound, unsound, cogent, or uncogent.

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Tutorial

Source: Image of Socrates, Creative Commons, http://bit.ly/29ZntMM; Image of Argument tree, Creative Commons, http://bit.ly/2bg82kq

Video Transcription

Hello, I'm Glenn, and this is the ethics tutorial for evaluating an argument. First, let's look at a couple of ideas to keep in mind and then cover the topics for this tutorial. Things to keep in mind for this tutorial are the evaluation method for the structure of deductive arguments and for inductive arguments.

In this tutorial, we'll be looking at how deductive arguments can be sound or unsound, and how inductive arguments can be cogent or uncogent. An effective way of doing this will be to look at a couple of tables with examples and see how they play out according to these categories.

Key terms to keep in mind for this tutorial are that a sound argument is one that is deductively valid with all true premises. An unsound argument is a deductive argument that is not sound or contains at least one false premise. A cogent argument is an inductive argument with all true premises. And an uncogent argument is an inductive argument that is not cogent or contains at least a false premise.

Understanding and delineating the different categories of arguments is really fairly simple when we put it into a chart format. As you can see from this first chart there is a limited number of possibilities. And once we determine one factor, we then have a further limited number of options available. So we start out with an argument, and we can see that any argument is either going to be deductive or inductive.

If we go down the path of deductive, we will see that then we are placed with the option of only having a valid or invalid deductive argument. If we have a valid argument, then our last options are to determine whether it's sound or unsound. If we have an invalid argument, we know that it must be unsound, our only option.

So if we go down the other path of inductive arguments, we are presented with the options of it being either strong or weak. If it is strong, then it can be further classified as cogent or uncogent. And if it's weak, it must be uncogent.

This is the basic structure of the arguments that we deal with in philosophy, and in ethics. And these are basically the only options available to us. It must fit here somewhere in the structure of this table.

So if someone says the argument presented to me is unsound, we know that it must be deductive because only deductive arguments could be sound, unsound, or unsound. And if it's unsound, we know it's either valid or invalid. However, if someone tells me that the argument presented to them is cogent, well we know that it's inductive and strong.

So depending upon the term that's used, we can figure out where it appears on this chart and what type of argument it is. Let's look at some specific arguments and see how we can classify them in their proper categorization as being inductive, deductive, valid, invalid, sound, unsound, strong, weak, cogent, and uncogent. And again, the easiest way to do this is to look at a table.

So here we have six arguments. Three of them are deductive, and three of them they're inductive. And we can see from this table how they fit into the classifications, which ones are relevant determinations, and which ones are irrelevant. So if we look at the first one, Jeff is a human. All humans have brains, therefore, Jeff has a brain.

We can see from its structure, and the use of certain words, that this is a deductive argument. Given the premises, the conclusion must follow from them. It's deductive. It is valid, and it is sound. It's soundness here is because the conclusion is true following from two true premises.

The conditions of it being strong, weak, cogent, or uncogent are irrelevant to this one because it is a deductive argument. Let's look at number three. The president must be 35 or older.

Obama is older than 35, therefore, Obama is the president. This is again, a deductive argument. It's much in the same structure as the first one, however, this is actually an invalid argument because, although, it seems OK that the conclusion follows from the premises, we can in fact very quickly construct what's called the counter example and show that it's not valid because it can lead to a false conclusion.

Just because Obama is older than 35 does not mean that he's the president. We could make this same claim 10 years ago, I mean, 10 years from now-- sorry-- in the future, and Obama would still be older than 35, but 10 years from now someone else will be president. So since it's deductive but can lead to a false conclusion, it is, therefore, invalid. And again, strong, cogent, and so forth are irrelevant to this because it is a deductive argument.

The next one, my cat purrs. My neighbor's cat purrs. All cats must purr. This is an inductive argument because the conclusion has a degree of probability, and it is not 100% certain.

It is also a weak argument because the conclusion that all cats must purr is an absolute statement about every cat in the world and that conclusion cannot be supported fully or even substantially by talking about my cat and the neighbor's cats. The truth about two cats cannot lead to a generalization about all cats in the world. Therefore, it is a weak argument and because it is weak, it is necessarily uncogent.

Remember from our previous chart, all weak arguments are uncogent. The next one the grave marker at Arlington National Cemetery says that "JFK is buried there." it must be the case that JFK is buried in that cemetery.

Again, this is an inductive argument. Validity and soundness are irrelevant to it. It is a strong inductive argument because the fact that there is a grave with JFK's initials on it, his name on it, in the cemetery leading to the belief that JFK is actually buried there is really convincing evidence. And it's cogent because it is in fact true that there is this grave there, and it is true that he is buried there. So it is a strong cogent inductive argument.

This chart, and using others like it, is very helpful in delineating the specifics of why an argument is deductive or inductive and how it fits the rest of the classifications. In review for this tutorial, we have explained how deductive arguments are sound or unsound, we have shown how inductive arguments can be cogent or uncogent. And through the use of a couple of useful tables, we have seen how these classifications fit into the different types of arguments and as they relate to the key terms for this tutorial.

Terms to Know
Cogent

An inductively strong argument with all true premises

Sound

A deductively valid argument with all true premises

Uncogent

An inductive argument that is not cogent

Unsound

A deductive argument that is not sound