Ich denke also bin ich (cogit ergo sum) - René Descartes

Pues tales frutos he recogido ya de ese método, que, aun cuando, en el juicio que sobre mí mismo hago, procuro siempre inclinarme del lado de la desconfianza mejor que del de la presunción, y aunque, al mirar con ánimo filosófico las distintas acciones y empresas de los hombres, no hallo casi ninguna que no me parezca vana e inútil

Nature teaches me that so many other bodies exist around mine of which some are to be avoided, some sought after.

Gratitude is a species of love, excited in us by some action of the person for whom we have it, and by which we believe that he has done some good to us, or at least that he has had the intention of doing so.

Passions, III, 193. XI, 473-474. Trans. John Morris