Nothing is to be accounted hostile force but where it leaves not the remedy of such an appeal [to the law], and it is such force alone that puts him that uses it into a state of war, and makes it lawful to resist him.
A man with a sword in his hand demands my purse on the highway, when perhaps I have not 12 pennies in my pocket.
This man I may lawfully kill.
To another I deliver 100 pounds to hold only whilst I alight, which he refuses to restore to me when I am got up again, but draws his sword to defend the possession of it by force. I endeavour to retake it.
The mischief this man does me is a hundred, or possibly a thousand times more than the other perhaps intended me (whom I killed before he really did me any); and yet I might lawfully kill the one and cannot so much as hurt the other lawfully.
The reason whereof is plain to see; because the one using force which threatened my life, I could not have time to appeal to the law to secure it, and when it was gone it was too late to appeal.
The law could not restore life to my dead carcass.
The loss was irreparable; which to prevent, the law of Nature gave me a right to destroy him who had put himself into a state of war with me and threatened my destruction.
But in the other case, my life not being in danger, I might Nature gave me a right to destroy him who had put himself into a state of war with me and threatened my destruction.
But in the other case, my life not being in danger, I might have the benefit of appealing to the law, and have reparation for my 100 pounds in that way.
John Locke, "An Essay Concerning the True Original Extent and End of Civil Government", Chapter 18 "Of Tyranny", #207, originally published in England, 1690.
Thanks for the quote from Locke who was, like our Founding Fathers, a product of the Enlightenmemt or Age of Reason (Note his reference to the law of Nature) and he clearly distinguishes when lethal force is justified (and when not) by law. Would that some of our present political leaders today had his clarity of thought.