One of the most interesting philosophers coming between these first greek philosophers and Socrates was Heraclitus. Unfortunatly we do not possess any extended work by him, but we do possess a number of his paradoxes which illustrate a sharp and observant mind. Two of these famous paradoxes are "The way up & the way down are one and the same." and "you can not step into the same river twice.". Carefully examined these paradoxes have much to do with the way language is actually used. Thus the river statement suggests everything is constantly in motion and that "sameness" is a catagory we impose for the conveniance of clasification. The paradoxes of Heraclitus emphasise the greek love of antithisis, the belief that defintion can occur only by means of opposites, an approach that has also been developed in our own times through the concept of "the other".
Socrates was born in 470 BC and died in 399 BC when he was forced to drink hemlock. It is important to note that Socrates has a rich tradition of systematic philosophy behind him. Like Jesus Socrates never wrote anything so far as we know, and for the thoughts of Socrates we are largely dependent on Plato an Xenophon. However neither wrote as a biographer. Plato in paticular writes as a philosopher who seeks to present Socrates as the ideal embodiment of philosophy, unjustly condemed by confusion with bogus philosophers (called sophists) and unjustly put to death for his dedication to the philosophical life.
Socrates occurs as a voice throughout the dialogs of Plato. Some of these dialogs are more obviosly historical of biographical than others. For example the Apology is an account of his defence at his trial when he had to face two accusatons:
The Phaedo (pronounced Fido) is a recreation of the final hours of Socrates in which he gives his proof for the immortality of the soul, and is shown dying with great dignity and fortatude. Unquestionably Socrates was responsible for enthusing Plato probably the greatest philosopher ever. But to what extent Socrates is presented in his own right in the dialogs of Plato, and extent he was used as a convenient voice we shall never be able to decide with any confidence. (Christianity of course faces the same problem with Jesus.)
Some of the things Plato has Socrates say, particularly concerning the docturin of Ideal Forms are manifestly annachronistic, for Socrates can not have possably held told them. We can however be certan of the way Socrates practiced philosophy. He practiced in public rather than private and necessaraly he associated with the young of the leisured classes and it is perfectly possible that one of the reasons that Socrates was indited in 399 BC was that he has strong associations with anti democratic forces in Athens, although it must be insisted that he at least in the Apology however supported the Atheniatica democratic institution. Very likely his whole philosophy revolved around two viewpoints in which what we call ethics and epistimolagy merged. The first of these viewpoints is "Virtue is wisdom or knowledge" and the second is "No one does wrong [the greek means literaly "misses the mark"] willingly". This implys that all wrong doing is due to lack of knowledge; virtue is knowledge.
In the dialogs a common critisism of the Socratic voice is that he is always negative and destructive, never positive, and this reflects what was very likely his practice of philosophy. That is to say, he would approch an "expert" and ask for the meaning of justice, or goodness, or piaty, or freedom, and similar abstract expressions, professing for himself complete ignorance. By question and answer he would then subject the replys to close analisis, the inevitable result being that the original "expert" would end up expressing and contradiction and so be forced to admit that he did not know at all.
Socrates was a familiar figure in the Athens of his day because of his approach, oral, in public, with the rich - he became associated with a new group of itinerant teachers (called sophits) in Greece in the second half of the 5th century BC who taught for money and with particular emphisis on the skills of public speaking. They aquired a dubious reputation (the comic poet Aristophanes refers to them "making the worst appear better") but in many ways they have been highly radical thinkers.
In one of his plays called "The Clouds" (420 BC) Aristophanes makes Socrates, presenting him as the owner of a thought factory, in which he lived in a basket as far away from earthly matters as possible (hence the title) where he taught young men who to avoid paying their gambling debts. This is a far cry from Plato, but only because of his association with Plato. Socrates is of overwelming but in the final thought undefinable importance in the history of philosophy.