Our knowledge of our own existence is intuitive. As for our own existence, we perceive it so plainly and so certainly, that it neither needs nor is capable of any proof. . . . I think, I reason, I feel pleasure and pain: can any of these be more evident to me than my own existence? . . . For if I know I feel pain, it is evident I have as certain perception of my own existence, as of the existence of the pain I feel: or if I know I doubt, I have as certain perception of the existence of the thing doubting, as of that thought which I call doubt. Experience then convinces us, that we have an intuitive knowledge of our own existence, and an internal infallible perception that we are. In every act of sensation, reasoning, or thinking, we are conscious to ourselves of our own being; and, in this matter, come not short of the highest degree of certainty.
John Locke (1632 - 1704)
Source: Essay Concerning Human Understanding, 1690
. . . whenever the Legislators endeavour to take away, and destroy the Property of the People, or to reduce them to Slavery under Arbitrary Power, they put themselves into a state of War with the People, who are thereupon absolved from any farther Obedience. . . . [Power then] devolves to the People, who have a Right to resume their original Liberty, and, by the Establishment of a new Legislative (such as they shall think fit) provide for their own Safety and Security, which is the end for which they are in Society.