The moon is made of green cheese. Therefore, cows jump over the moon. Either Colonel Mustard or Miss Scarlet is the culprit. Miss Scarlet is not the culprit. Hence, Colonel Mustard is the culprit.
All engineers enjoy ballet.
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.