'If it really were impossible to derive an ought from the is of the human design, then the practice of medicine would make no sense. Neither would the practice of health education. Consider the young glue-sniffer again. How should we advise him? Is the purpose of his lungs irrelevant? Should we say to him, "Sniff all you want, because an is does not imply an ought"? Of course not; we should advise him to kick the habit. We ought to respect the is of our design. Nothing in us should be put into action in a way that flouts its inbuilt meanings and purposes.'
J Budziszewski, On the Meaning of Sex, p.22.
