Félix Nadar, Autoportrait tournant (c. 1865, Bibliothèque Nationale de France).
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«For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe anything but the perception. (…) If anyone, upon serious and unprejudiced reflection thinks he has a different notion of himself, I must confess I call reason no longer with him. All I can allow him is, that he may be in the right as well as I, and that we are essentially different in this particular. He may, perhaps, perceive something simple and continued, which he calls himself; though I am certain there is no such principle in me».
---David Hume (1739).