Therefore, some males enjoy ballet. Sometimes an author will not explicitly state all the premises of his argument. This will render his argument invalid as it is written. Therefore, some males enjoy ballet. is invalid. But it's clear how to fix it up.
Some engineers are male.
Therefore, some males enjoy ballet. You should become adept at filling in such missing premises, so that you can see the underlying form of an argument more clearly. Therefore, if you keep driving your car with a faulty carburetor, you will eventually get hurt. Abortion is morally wrong. Abortion is not a constitutional right.