No A are B. Some C are B. So, no A are C

Question

   Is this a valid or invalid form? Briefly explain your answer.

 Put a substitution instance into the form in ‘a’ above.

  Identify and explain two (2) major weaknesses of using the five famous forms.

Answer 1

To discern the answer, consider the basic rules of validation for categorical logic. Among the handful is one that says "If one of the premises is particular, then the conclusion must also be particular." We have one particular premise, "Some C are B," but the conclusion is universal. Therefore, we see that this fails to meet the basic rules of validation.

It can also be shown to be invalid using Euler Circles, though this approach can lead to error if one is not careful. If you draw this out (or work through some examples), you will find that it is possible for the premises to be true and the conclusion to be false, which is the contemporary definition of an invalid argument.