When Hegel talked about dialectic instead of just using it, he occasionally made it sound as if dialectic governed events in the world. This is a loose, popular way of speaking that should not be taken literally. Dialectic is the main tool of the forward progress of philosophical criticism, and thus indirectly helps refine our understanding of the world and events in it. It could not directly drive events.
It is actually very hard to draw a sharp line between the world “in itself” and our understanding of it, because our understanding (in the general, not the specifically Hegelian sense) is all we actually have to go on. Our sense of the world in itself is permeated by artifacts of our understanding, because it comes entirely from our understanding.
But then it turns out that our understanding is not just some private, subjective thing of ours. Our understanding participates in the world, and is part of it. The cultivation of shareable thought grounds objectivity in (our sense of) the world. Much of the content of shareable thought comes to us from outside. In a poetic manner of speaking, it could be said that the world thinks itself through us. But in a more direct way, we are the agents and stewards of the world’s thought. In particular, it advances through us. There is thus no wall between our understanding and the world. There is a meaningful distinction, but the content of shareable thought straddles the boundary, so to speak.
Aristotle’s version of dialectic is much less famous nowadays, but a great deal easier to understand, and it does not require apologetics of the sort I just provided for Hegel’s. It uses logic and semantics to analyze the meaning of things said, making no assumption whether or not they are grounded in knowledge.
Aristotle explicitly said (Topics, book 1) that this is the way to investigate first principles (i.e., starting points) of knowledge. With respect to such starting points, we have no possibility of knowledge in the strong sense (episteme) — which requires development — but only a kind of initial personal acquaintance or familiarity (gnosis), as he said in Posterior Analytics.
There has been a strong tradition of misinterpretation of this latter passage. With no textual basis, many people who wanted to read Stoic-style foundationalism back into Aristotle — or were influenced by others with this sort of motivation — have glossed Aristotelian gnosis as something like a strong intellectual intuition, and claimed Aristotle was saying first principles of knowledge were better known in a strong sense, rather than just more familiar. (See also Aristotelian Demonstration.)
Aristotle’s actual practice, however, confirms the reading of first principles of knowledge as themselves objects of mere familiarity rather than strong knowledge. (Aristotle’s loftier principles are ends, not starting points of knowledge, and he typically places discussion of them at the end of an inquiry.) His starting points for inquiries are very pragmatic. He typically begins an inquiry with logical/semantic (i.e., “dialectical”) analysis of widely known opinions on the subject. He also explicitly recommends that we begin any inquiry from what is closer to us, and then, through analysis, refine our understanding. (See also The Epistemic Modesty of Plato and Aristotle).
The development of knowledge starts from what is close to us and easier to grasp, and becomes progressively more secure through the dialectical work we do on it. Aristotelian dialectic uses the same logical forms as demonstration, but is mainly concerned with inferential semantic analysis rather than deriving conclusions. (Even Aristotelian demonstration is concerned not so much with deriving conclusions, as with perspicuously showing their basis.) Aristotle does the great majority of his actual work with dialectic rather than demonstration.
Once one becomes familiar with the profile of the Aristotelian version, it becomes possible to see something very like it at the core of Hegel’s way of working — not so much in what he says about it, as in what he does. (See also Aristotelian Dialectic; Dialogue; Scholastic Dialectic; Contradiction vs Polarity; Three Logical Moments.)