Deductive Validity: Definition & Examples

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  • 0:03 Definition of…
  • 1:00 Example Argument #1
  • 1:43 Example Argument #2
  • 2:36 Example Argument #3
  • 3:40 Example Argument #4
  • 4:09 Lesson Summary
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Lesson Transcript
Instructor: J.R. Hudspeth

Jackie has taught college English and Critical Thinking and has a Master's degree in English Rhetoric and Composition

Deductive validity is a term for an argument that holds up logically and has factual information. Learn more about deductive validity's definition and see some examples of how deductive validity can help us analyze whether or not an argument is well-made!

Definition of Deductive Validity

Deductive validity describes arguments that are both factual and logical. Any argument that doesn't have facts that are actually true or that are not logically sound will not pass the test as a good argument. It is important to be able to determine whether or not an argument is valid because invalid arguments are bad and should not be accepted. If you are writing an argumentative paper, you must make sure that your arguments are valid.

There are two things that make an argument valid:

  1. The facts, also known as the premises, must be correct.
  2. Your analysis of the facts, also known as the conclusion, must hold up logically.

We will look at arguments that fail each of those things and that are invalid. Then, we will look at an argument that includes both of those things and is valid.

Example Argument #1

Let's look at the facts and analysis of our first sample argument:

FACT/PREMISE #1: Everyone who goes to school will definitely get a degree.

FACT/PREMISE #2: John goes to school.

ANALYSIS/CONCLUSION: John will definitely get a degree.

Here, the problem is that one of our facts is not true; not everyone who goes to school will finish and earn a degree. Because that fact is not true, our argument doesn't hold up. We cannot conclude that John will definitely get a degree just because he goes to school; he will still have to complete school to earn a degree.

Example Argument #2

Let's look at another example of an argument that is not deductively valid because one or more of the facts is not true.

FACT/PREMISE #1: Everyone who has ever been imprisoned is a bad person.

FACT/PREMISE #2: Nelson Mandela was imprisoned.

ANALYSIS/CONCLUSION: Nelson Mandela was a bad person.

Again, we see that our first fact is not true. Everyone who has ever been imprisoned is not necessarily a bad person. Therefore, the whole argument does not hold up. You can see that having incorrect facts or making sweeping generalizations and presenting them as fact can often make an argument invalid.

What about when the facts are right, but the conclusion is not valid? Let's look at this example.

Example Argument #3

FACT/PREMISE #1: Cats have four legs.

FACT/PREMISE #2: Cats are mammals.

ANALYSIS/CONCLUSION: Mammals have four legs.

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