Hume came close to an evolutionary interpretation, even perceiving that 'no form can persist unless it possesses those powers and organs necessary for its subsistence: some new order or economy must be tried and so on, without intermission; till at last some order which can support and maintain itself, is fallen upon'; and that man cannot 'pretend to an exemption from the lot of all living animals [because the] perpetual war among all living creatures' must go on (1779/1886:11, 429, 436). As has been well said, he practically recognised that 'there is a third category between natural and artificial which shares certain characteristics with both' (Haakonssen, 1981:24).