IMHO, it was Aristotle's discovery of the syllogism that really got things going.
Socrates was stuck in a rut. He would spend a whole day on a definition. But he couldn't use the next day because another Sophist might flip the definition upside down.
Plato had his forms which indicated that there is some validity to the ideas rushing around in our heads.
Aristotle's focus on the form of arguments made it so people could start building larger world views. This made it possible for Zeno of Citium and his followers to devise the Stoic Philosophy.