Folks like Aristotle, Isocrates, and Plato didn't just pop up overnight. Nor were they dropped from a flying saucer. They picked up on the philosophical approaches of those that preceded them and expanded on them. Here are some of those thinkers.
Heraclitus (b. 535 B.C., d. 475 B.C.)
Heraclitus, an aristocrat, was the progenitor of the Sophists. He was a skeptic and was suspicious of any knowledge gained from our senses/perception. Heraclitus argued that "change is persuasive." His argument can be set down as follows:
The Heraclitean doctrine of opposites begins with the State of Becoming. Heraclitus argues that all things contain two qualities: being and non-being. The material substance that makes up what we call things is made up of the conflict between being and non-being. Change is produced through movement from non-being to being. The normal state between the two forces is harmony, but fire "strife" is the creator of all things by creating the necessary conflict. His most famous statement is: "You can't step in the same river twice."
Parmenides (b. 514 B.C. d.??)
Parmenides was the thinker that begat Aristotle. Parmenides could care less about change. He focused on being. His first principle is: "Within Being there is no change - no past/present/future. Being is eternal. It has no beginning nor end." Parmenides contrasts being with appearance (that which is gained through our senses/perception). Being can be known only through reason. He holds that the world of falsity, illusion, and change (doxa- gr. for opinion and perception) is the contrast of being. Yet we can never reach the perfection that is being, all we can do is approximate that perfection through reason. Parmenides argues that Justice is a form of being.
Aeschylus (b. 525-d. 485 B.C.)
Aeschylus was a dramatist. He was the first to use costuming and multiple actors in plays. Before Aeschylus, tragedy was a struggle against fate -- the interest was in the struggle itself. Aeschylus, although still Homeric in attitude, focused on the dangers of excess; of crimes marked by overstepping the bounds of diving justice. So, the focus was on ethics instead of the battle.
Euripides
Another dramatist, his works are still relevant today. In Medea he wrote of the destruction and sorrow of war, as well as the treatment of women and non-Greeks. In Orestes he wrote of the moral degeneracy of the aristocratic class. He was the first writer to develop characters that were directly relevant to the audience (realism). He wrote in favor of reason and against abuses of power. Was the first social critic.