philosophy- analysing arguments

Question

determine whether the argument is valid, and give a reason why.

Punishment for crime is never justified. This is because we know from a great deal of carefully assembled and analysed empirical data that punishment is not a deterrent. And punishment for crimes is justified if it actually deters people from committing them.

The argument is valid, the premises are true, so the conclusion is also.

The argument is valid, follows the valid form of modus tollens.

The argument is valid, if the premises are true, it's impossible for punishment to be justified.

The argument is invalid, punishment might still be a deterrent.

The argument is invalid, it commits the fallacy of denying the antecedent - there might be other reasons why crime is a deterrent.

The argument is invalid, even if the premises were true, punishment might still be justified for other reasons.

Choose the generalised form that represents the argument.

A = punishment is justified

B = punishment deters people from committing crimes

Answer 1

Hi Rose,

This argument looks invalid. The argument is as follows:

Premise 1: If punishment deters people from committing crimes, then punishment is justified.

Premise 2: Punishment does not deter people from committing crimes.

Conclusion: Therefore, punishment is not justified.

The form of this argument is as follows:

A = punishment is justified

B = punishment deters people from committing crimes.

P1: If B then A

P2: ~B

C: ~A

This form of argument is invalid. Denying B is not enough to conclude ~A. Practically, we can see this is the case in the fact that punishment might be justified for reasons other than its use as a deterrent. For example, punishment might be justified because it is the morally right thing to do.

We can see this in a more trivial example:

P1: If it rained last night then the ground is wet.

P2: It did not rain last night.

P3: Therefore the ground is not wet.

This is an invalid argument. The ground may be wet for any number of other reasons! Maybe the sprinklers went off, or a someone spilled their drink etc.