Plato established a set metric for morality, and good, through his use of the Forms (Moore & Bruder, 2005, p. 255). Importantly the form of "Good" was the highest form; the counterpart of this was evil and nonexistence (Moore & Bruder, 2005, p. 257). It was then through reason, and seeking knowledge of the form of Good, that served as the basis for his ethic (Moore & Bruder, 2005, p. 257). Aristotle took an alternative viewpoint and made an appeal to nature, and that good is following our natural objective (Moore & Bruder, 2005, p. 261). Aristotle reasoned that the natural objective for humans was happiness which can be achieved through enjoyment and enhancing the ability to reason (Moore & Bruder, 2005, p. 261).
Augustine and Aquinas expanded upon, and modified where necessary, Plato 's and Aristotle 's philosophies adding God as the focal point (Moore & Bruder, 2005, p. 267 & 273). Importantly both Augustine and Aquinas continued with a metaphysic for their philosophy. Hobbes extended upon Aristotle 's naturalism though his materialism belief that only the physical exists, and thus morality flowed from this (Moore & Bruder, 2005, p. 274-275). Kant followed both Plato and Aristotle that reason played an integral role in philosophy (Moore & Bruder, 2005, p. 278). Nietzsche, and the other existentialist philosophers, rejected the previous
References: Moore, B. N. & Bruder, K. (2005). Philosophy: The power of ideas. New York: McGraw-Hill.