A deductive argument consists in part of a premise and a conclusion. These are the parts of the argument that are important for validity and soundness. A valid argument is one where the conclusion has to be true if the premise is true. A sound argument is one that is valid and in which the premise is actually true.
Therefore, a deductive argument that is valid but not sound might be:
- Only teachers have black hair.
- I have black hair.
- Therefore, I am a teacher.
This is valid because I would have to be a teacher if my hair is black and only teachers have black hair. But it is not a sound argument because there are plenty of people who have black hair and are not teachers. Therefore, the premise of this argument is not actually true.