THE EVALUATION OF ARGUMENTS
Much of philosophy is concerned with the evaluation of arguments.  You will often find it helpful both in thinking about issues and in writing papers to formalize the arguments that you are discussing into premises and conclusions and to assess them systematically.  The following concepts and examples may help you evaluate arguments.

DEFINITIONS
An argument is a set of statements one of which -- the conclusion -- is supposed to be supported in some way by the others -- the premises.  Arguments are of two basic kinds: deductive or deductively valid arguments and non-deductive arguments.

Deductively valid arguments are of two kinds: valid arguments and sound arguments.  Valid arguments are arguments such that if their premises were true, then their conclusions would have to be true.  In other words, they are arguments such that it is impossible that their premises should all be true and their conclusions false.    A sound argument is a valid argument all of whose premises are true.

Truth is a property of premises or statements, not arguments.  Validity is a property of arguments, not premises or statements.  Soundness, like validity, is a property of arguments, not premises or statements.

In philosophy, it is often possible to find or construct arguments that purport to be sound (i.e. valid arguments with true premises).  When you come across such an argument with an apparently implausible conclusion, you have reason to believe that something has gone wrong somewhere.  But be sure to explain where things have gone wrong.  In most debates, one can divide critical responses into two main kinds -- Oh Yeah? and So What?  The So What? response concedes the conclusion in question, if only for the sake of argument, but denies that the conclusion has the consequences or significance that its proponents allege.  The Oh Yeah? response challenges the cogency of the argument in support of the conclusion.  One can challenge the soundness of an argument by challenging either the truth of its premises or the validity of its inferences (or both).

Non-deductive arguments are those arguments that are not deductively valid.  The set of non deductive arguments includes, but is not exhausted by, fallacious arguments (i.e. arguments that purport to be deductively valid, but fail), inductive arguments, arguments by analogy, and arguments to the best explanation.  There are both good and bad non deductive arguments.  What the exact criteria are for good non deductive arguments is a matter of controversy.

EXAMPLES
A.

1. All persons are mortal.
2. Socrates is a person.
3. Therefore, Socrates is mortal.

B.

1. All pigs can fly.
2. Socrates is a pig.
3. Therefore, Socrates can fly.

C.

1. All dogs are mortal.
2. Spot is a dog.
3. Therefore, Spot will die by the age of 25.

D.

1. This urn contains 999 red balls and one black ball.
2. Therefore, the first ball picked from this urn will be red.

E.

1. Those tracks outside the chicken coop were made either by a dog or by a wolf.
2. No one has ever seen a wolf this far south.
3. Therefore, those tracks were made by a dog.

F.

1. Justice in the state requires rule by the rational class.
2. Therefore, justice in the soul requires rule by the rational part of the soul.

G.

1. It’s reasonable to do things that are beneficial.
2. Exercise is beneficial.
3. Hence, exercise is reasonable.
4. Charitable contributions are beneficial.
5. Hence, it’s reasonable to make charitable contributions.

H.

1. The value that an action would produce provides reason to perform it.
2. The more value an action would produce, the more reason there is to perform it.
3. The right thing to do is the action that one has most or strongest reason to perform.
4. Hence, the right thing to do is the action that would produce the most value.

I.

1. The value that an action would produce provides reason to perform it.
2. The more value an action would produce, the more reason there is to perform it.
3. The best thing to do is the action that would produce the most value.

J.

1. If Socrates corrupts the youth, he does so either willingly or unwillingly.
2. If he does so unwillingly, he ought to be privately educated so as not to corrupt.
3. If he does so willingly, he ought to be punished.
4. Anyone who corrupts willingly harms those whom he corrupts.
5. Anyone willingly harmed is likely to harm his harmer.
6. No one willingly risks harm.
7. Therefore, no one willingly corrupts anyone.
8. Therefore, Socrates does not willing corrupt anyone.
9. Therefore, if Socrates corrupts, he corrupts unwillingly.
10. Therefore, if Socrates corrupts, he ought to be privately educated so as not to corrupt.

K.

1. All things come to be from their opposites.
2. Hence, death comes to be from life.
3. Hence, that life came from a previous death.
4. Hence, that previous death came from a previous life.
5. Hence, there is an eternal recurrence that assures my persistence beyond death.