There are two kind of disagreement:

1. In my speech a given sentence A is stated to be true, while in your speech the same sentence A is stated to be false.
2. In my speech a given sentence A is stated to have a truth value, while in your speech A is senseless: it can be neither true nor false.

The disagreement between science and dialectic is of the kind (B) or of the kind (A) ?

When committed to show that no conflict there is, Marxists mostly presuppose the conflict to be of the kind (A): dialectic doesn't turn false what science says it is true; it just takes science as a part of a larger system; a system which is able to grasp the teleological movement of history - and that, at least, locates science at the level of an instrumental thought or of a store of partial representations in wanting of a more comprehensive view.

But what is dialectic ?

Here you are some meanings I know:

1. A flexible thought, able to pursue the changeable movements of a living experience
2. Historical reason against normative reason.
3. An investigation concerning the posits of a thought
4. The ascending proceeding, having a direction and an internal finality, of reality as a whole
5. The philosophical discourse, whose task is to grasp this ascending proceeding of reality (fulfilling the task, the philosophical discourse turns a subjective assumption - the subjective assumption that such an ascending proceeding there is - into an objective truth)
6. The subjective/objective character of reality: what seems a chrema (a solid thing) is a pragma (the result of actions, will, projects, thought etc. )

A. Toson