Why do we still learn about sophists in philosophy if literally everything about them is outdated? It's important to know how the theories evolved over time as to not fall into the same trappings as those before. Those who forget history are.... you know the rest.
Also, he did have a few good points... he diagnosed the problem pretty well, but his solutions aren't feasible.
Also, he did have a few good points... he diagnosed the problem pretty well, but his solutions aren't feasible.