Invalid Argument/Examples/Socrates is Mortal

Example of Invalid Argument
This argument is technically invalid:


 *  is a man.
 * Therefore, is mortal.

Proof
It may be thought that the conclusion may hence be deduced from the premise.

However, this does so purely because of the a priori knowledge that:
 * if $A$ is a man, then $A$ is mortal.

Hence while the conclusion follows from the premise, this does not happen purely by means of deduction from the argument itself.

Let $P$ denote the simple statement  is a man..

Let $Q$ denote the simple statement  is mortal..

The argument can then be expressed as:

But this is not a valid argument form.