"In every system of morality which I have hitherto met with, I have always remarked that the author proceeds for some time in the ordinary way of reasoning and establishes the being of a God or makes observations concerning human affairs,when of a sudden I am surprised 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 expresses some new relation or affirmation, it is necessary that it should be observed and explained, and at the same time that a reason should be given for what seems altogether inconcievable, how this new relation can be a deduction from others which are entirely different from it. But as authors do not commonly use this precaution, I shall presume to recommend it to the readers, and am persuaded that this small attention would subvert all the vulgar systems of morality and let us see that the distinction of vice and virtue is not founded merely on the relation of objects, nor is percieved by reason." David Hume A Treatise on Human Nature, Section I, pgs. 247-248 Modern Library ed.