•Validity is a huge concept. It is the centerpiece of discussion when it comes to all deductive arguments.
•An argument is valid just in case the argument is structured in such a way that if the premises are true, then the conclusion must also be true. To put it another way, if the premises are true, there is no possible way that the conclusion can be false.
•Popular validity and logical validity
•Mind you that the definition I provided above is not the popular concept of validity. We sometimes just use the term “valid” as a word for legitimate. So, for example, we would not say that telling the teacher that the dog ate your homework is a valid excuse. (A goat maybe, not a dog). Nevertheless, that excuse can be made into a valid argument.
Let’s take this argument:
•If I say my dog ate my homework, then I have a valid excuse.
•I say that my dog ate my homework.
•Therefore, I have a valid excuse.
This is a valid argument, according to the logical definition of “valid” because if the premises are true, the conclusion must be true. Most of us would agree that the conclusion is false. But that is because we are inclined to reject the first premise. If the first premise were true, and the second also, then the conclusion would have to be true. The argument is valid (logical sense) even though the excuse is not (popular sense).