Deductive, valid but unsound

This argument is such that it is impossible for the premises to be true and at the same time the conclusion false. However, that is hypothetical since, in the actual world, one or more of the premises are false.

Consider:

If Superman actually exists then at least one superhero is real.
Superman actually exists.
At least one superhero is real.

The inference is OK--that is the inference is valid. If the two premises are true, then the conclusion is also true. However, the second premise is false--there is no Superman.

Validity is a way of appraising the inference from premises to conclusion. Soundness adds the second dimension of whether or not the premises are true in addition to the argument being valid.

Sound = Valid + True Premises. So, a valid argument with one or more false premises is unsound (not sound).