  The duty of allegiance to our present governors does not depend upon their or their ancestors’ divine right to govern, Hume says, nor on any promise we have made to them or any contract that transfers rights to them, but rather on the general social value of having a government.  Rulers thus need not be chosen by the people in order to be legitimate.  Consequently, who is the ruler will often be a matter of salience and imaginative association; and it will be no ground for legitimate rebellion that a ruler was selected arbitrarily.  Rulers identified by long possession of authority, present possession, conquest, succession, or positive law will be suitably salient and so legitimate, provided their rule tends to the common good.  Although governments exist to serve the interests of their people, changing magistrates and forms of government for the sake of small advantages to the public would yield disorder and upheaval, defeating the purpose of government; so our duty of allegiance forbids this.  A government that maintains conditions preferable to what they would be without it retains its legitimacy and may not rightly be overthrown.  But rebellion against a cruel tyranny is no violation of our duty of allegiance, and may rightly be undertaken.  