Dialectics is the ability to argue both sides of a proposition -- a skill needed by politicians who wanted to convince others to support their positions. Protagoras brought dialectics to its classic form when he invented “eristics“, a debating method designed to confuse an opponent by taking points he had already conceded. Marrou calls this a combination of brazen cynical pragmatism and astonishing practical effectiveness.
The historical significance of dialectics is hard to overstate given its influence on the whole of Greek philosophy, science, and culture.