In DG dependencies are basic elements in a sentence's structure, whereas in other theories they may be only implicit - e.g. it may be possible to identify a phrase's head as the daughter which has the same features as the mother. In many languages this allows extremely general word-order rules because all dependents stand on the same side of the head of their phrase. Dependencies are always relations between two parts of a larger whole, never between the whole and one of its parts. The latter relation is constituency . In some versions of DG constituency relations play no part at all in syntax, which means that phrases play no explicit part and the only unit of grammar is the word.
Subject is a kind of dependent.
The only justification for recognising a dependency between A and B is the existence of a rule which makes some property of one sensitive to some property of the other. Since word order is not tied directly to dependency rules, it is easier to write grammars for, e.g., Latin. The point here is that DG allows for an easier factoring of linear order out of hierachical structure. This makes the syntactic structures simpler. Together with the fact that Lexicase is a very constrained theory even when compared to other DGs, this provides evidence for our general approach.