Without going into detail I would refer you to Derrida's attack on the "metaphysics of presence". What we call "objectivity" is a contextual construction of the dynamics of communication. Objects have no context independent status. ("Fact" from facere-to construct)
The terms subjects and objects (and units) are abstract. The whole point of abstract is to have context independent status.
When we say "a ball is an object," it doesn't matter what the context is, balls are always objects. When we say, "shall we change the subject," it doesn't matter what subject we are talking about, we want it changed. This is the point of having abstract terms, they are context independent.
Abstraction is, like Fil was trying to say, existential.
I believe Derrida is using the word "objectivity" because it is abstract but what he means is its reduction into a particular.
Aren't subjects, objects, units and relations abstract? Aren't abstract concepts context independent?