> In meta-ethics, the is-ought problem was raised by David Hume, who
> noted that many writers make claims about what ought to be on the
> basis of statements about what is. However, there seems to be a
> significant difference between descriptive statements (about what is)
> and prescriptive statements (about what ought to be).
>
> Hume discusses the problem in book III, part I, section I of his A
> Treatise of Human Nature:
>
> “ In every system of morality, which I have hitherto met with, I have
> always remark'd, that the author proceeds for some time in the
> ordinary ways of reasoning, and establishes the being of a God, or
> makes observations concerning human affairs; when all of a sudden I am
> surpriz'd to find, that instead of the usual copulations of
> propositions, is, and is not, I meet with no proposition that is not
> connected with an ought, or an ought not. This change is
> imperceptible; but is however, of the last consequence. For as this
> ought, or ought not,that expresses some new relation or affirmation,
> 'tis necessary that it shou'd be observ'd and explain'd; and at the ...