Socrates was a postmodernist. Socrates was on a mission toward wisdom, or at least some truth, and the first step in his journey was to admit to himself that he couldn't be sure that any conventional wisdom contained either wisdom or truth. On the wisdom front, well, Athenian society had its issues but was conventionally thought to be run by her best and brightest--experts in their fields--wise men. Socrates, one by one, asked the best and brightest to explain themselves--to enunciate their wisdom--and then tested their utterances for truth. The wise men of Athens were demonstrated to be...lacking.
In his maddeningly round about way, Socrates was the first lover of wisdom who took upon himself a task to publicly "question authority." While he never managed to find wisdom, he found a way to reveal it: admit your misgivings and deficiencies and attempt to overcome them. His method, god help us all, was to subject every idea of knowledge to an existential hole-punch and turn conventional wisdom--and even common sense--into a sieve. Thus far the great colander of wisdom remains largely empty, but a shit ton of mistaken notions of truth have at least been strained and shown the drain. Socrates deconstructed Athenian "high-culture," took his medicine, and left Plato to make something of the pieces.
Plato did something really interesting with the tattered mess he was left with. Unlike Socrates, Plato wasn't just a fucking critic of false wisdom. Plato wanted to discover Truth. But all around him was the collection of broken examples that Socrates seemed to take some great ironic pleasure in taking apart. Still, in every concept Socrates dismantled, in every attempt by his contemporaries to expound them, Plato found some aspect of truth. "This concept of justice," Plato pondered, "might not be the whole truth, but it holds an element of Truth." There's a certain "truthiness" to societal norms, cultural norms, conventional wisdom. Not Truth, exactly, but the best yet cut at it. Plato has a modern counterpart, though I can't put my finger quite on who it might be.
In Plato's time, the sophists ruled. Word-smiths, argument makers, narrative keepers held the power to influence the halls of governance, and to sway the polis. Plato watched as Socrates rendered the best and brightest of the "gate-keepers" of wisdom and truth into drippings from the strainer. What he saw left behind, previously though to be the refuse, the stuff to be discarded, was the Form of Truth. The Form of Justice. The Form of Wisdom. What Plato saw among the refuse left behind by Socrates was the FORMS of all things toward which a social creature and its social organizations OUGHT to be striving.
The sophists with whom Socrates argued were all about "wining friends and influencing [the] people," and Socrates revealed them as fakers. Plato looked deeper into the object of the argument and revealed its Ideals. What is Justice? I don't know, but there's a bit of truth in every effort to parse it. Socrates saw through the sophists of the Athenian expert class and shatter the appearance of wisdom that they enjoyed. Plato sow through Socrates, his project of deconstruction, and attempted to build an Ideal. Plato RECONSTRUCTED wisdom and truth by admitting that neither can ever exist among mere men, but can be striven toward. We might never know Justice, but we can know injustice, and strive to better define Justice through elimination.
The sophists were Modernity, Socrates was Post-modern, and Plato was attempting a synthesis. And the whole fucking project began again with Aristotle. And again. And again.