include Protagoras, Gorgias, Hippias, Thrasymachus, Prodicus, Callicles, Antiphon, and Critias. Protagoras is mostly known for two of his quotes. One is that "[humans are..] the measure of all things, of things that are that they are, of things that are not that they are not" which is commonly interpreted as affirming philosophical relativism, but it can also be interpreted as claiming that knowledge is only relevant to humankind, that moral rightness and other forms of knowledge are relevant to and limited to human mind and perception. The other quote is, "Concerning the gods, I cannot ascertain whether they exist or whether they do not, or what form they have; for there are many obstacles to knowing, including the obscurity of the question and the brevity of human life." Gorgias wrote a book named On Nature, in which he attacked the Eleatics' concepts of What-is and What-is-not. He claimed it is absurd to hold that nonexistence exists, and that What-is was impossible since it had to either be generated or be unlimited and neither is sufficient. There is an ongoing debate among modern scholars whether he was a serious thinker, a precursor of extreme relativism and skepticism, or merely a charlatan. Antiphon placed natural law against the law of the city. One need not obey the city's laws as long as one will not get caught. One could argue that Antiphon was a careful hedonist—rejecting dangerous pleasures. Philolaous of Croton and Diogenes of Apollonia Philolaus of Croton and Diogenes of Apollonia from Thrace (born c. 460 BCE) are considered the last generation of pre-Socratics. Rather than advancing a cosmological perspective on how our universe is constructed, they are mostly noted for advancing abstract thinking and argumentation. Pythagorianism, Anaxagoras and Empedocles influenced Philolaus. He attempted to explain both the variety and unity of the cosmos. He addressed the need to explain how the various masses of the universe interact among them and coined the term Harmonia, a binding force that allows mass to take shape. The structure of the cosmos consisted of apeira (unlimiteds) and perainonta (limiters). Diogenes of Apollonia returned to Milesian monism, but with a rather more elegant thought. As he says in DK64 B2 "It seems to me, overall, that all things are alterations of the same things and are the same thing". He explains that things, even when changing shapes, remain ontologically the same. Topics Knowledge The mythologoi,