1 of 1

Write now Article Tools

One of the most difficult insights for students to grasp about the concepts of soundness and cogency is that they cannot always be determined. I have noticed that when students evaluate arguments they sometimes feel the need to state that an argument is sound or unsound, cogent or uncogent when they cannot possibly have any means of truly determining this. Let's look at the concepts closer and try to understand why they sometimes cannot determined.

The definition of a sound argument is one that is valid and has true premises. A cogent argument is one that is strong, has true premises, and does not omit any premises that would entail a different conclusion from the one drawn in the argument. In deductive arguments that are valid, the determination that the argument is unsound simply means that the premises are false. In an inductive argument that is strong, the determination that the argument is uncogent simply means that the premises are false. Of course, an invalid argument is automatically judged unsound just as a weak argument is automatically uncogent.

With these parameters in mind let's look at some examples.

Since Moby Dick was written by Shakespeare and Moby Dick is a science fiction novel, it follows that Shakespeare wrote a science fiction novel. In this deductive argument the premises (assumed true) necessarily entail that the conclusion is true so the argument is valid. Once we determine this we ask whether the premises are really true or false. In this example the premises are false so the argument is unsound. That should be easy enough.

But, consider this example. Since Agatha is the mother of Raquel and the sister of Tom, it follows that Tom is the uncle of Raquel. Again this is a valid argument so we need to determine (if possible) soundness. But, ask yourself the question: Are these premises really true? You might say yes, but how do you know? You might say we don't know so the argument is unsound. But wait! Judging an argument unsound simply means that the premises are false. Do you know this to be the case either? No. Here is a case where the truth of the premises cannot be determined so soundness cannot be determined. What would be the proper answer to this question then? We would say it is deductive and valid but the soundness cannot be determined. Sometimes in logic "I don't know" is the right answer!

This also occurs in inductive arguments. Consider this example. Coca-Cola is an extremely popular soft drink. Therefore, probably someone, somewhere

• 1
• 2
• next page >>

Add your voice

Know something about Determining soundness and cogency in logic?
We want to hear your view. Write now!