Presumptions are normative instruments for injecting some make-believe into an all too real world, with the long-term hope that reality may become more like make-believe.
Because academic writing is generally discursive, which is to say, because it is done "for the sake of argument", its sentences are often marked by the nesting of qualifying clauses. These clauses condition the way we read the main clause; they determine "the sense in which" we are to take it. The use of subordinating conjunctions to coordinate clauses (also called hypotaxis) is very common in academic writing because it makes the logical hierarchy of the clauses explicit. Consider, as an example, the first sentence in this paragraph. These clauses could be arranged very differently. We could, for example, resort to parataxis, which is the arrangement of clauses without subordinating conjunctions, and which often results in a bad parody of Hemingway's prose.
Academic writing is generally discursive. It is done "for the sake of argument". Its sentences are often marked by the nesting of qualifying clauses.This exercise will be familiar to most people who have struggled explicitly with the problem of writing in any language. I bring it up here for a specific reason. Paratactical presentation brings the individual propositions that a sentence deploys to the fore, while hypotactical presentation makes a single gesture of their arrangement. While your writing will generally strive for such coherent gestures, the awareness that paratactical presentation brings can be useful in locating important elements of your style.
Philosophers sometimes count beliefs among the "propositional attitudes", meaning that beliefs, like hopes, desires, promises and fears are "of" or "about" something. It is important to keep in mind that propositions themselves are not necessarily to be believed. Believing is one thing you can do with a proposition; but there are other things. One can, for example, presume it.
Consider again the propositions of the first sentence of this post. Which may be presented in a still more radically paratactical form to allow each of them to stand entirely on their own.
1. Academic writing is generally discursive.While I believe the original sentence to be basically true, and even largely "good", I feel very differently about these propositions when taken in isolation. The third sentence, for example, which had previously emerged as an understandable feature of a specific context of writing (specific features of which had been highlighted) now stands as a terse judgment about the style of academic texts. Thinking about it on its own, I find myself wanting to add the words "more often marred" in parenthesis after "marked". Also, the first two propositions, and especially the second, are, a bit dubious in today's "publish or perish" world . ("Discursive" still holds in one sense, but not in the sense specified by the original subordination of clauses.) The sense of practical advice and amiable engagement is lost in the paratactic presentation and is replaced with an air of detached judgement. This effect is in fact what parataxis is often associated with. It is "terse" .
2. Academic writing is done for the sake of argument.
3. The sentences of academic texts are often marked by the nesting of qualifying clauses.
Steve Fuller  has taught us to think of our theories as systems of presumption not belief. He uses the presumption of innocence in legal procedings as a paradigm case. After all, to presume that the accused is innocent is not to believe that he hasn't committed the crime. It is not inconsistent with the procedural presumption to suspect that he is guilty, or even to believe this quite firmly. Opinions will differ, and some will be more sure than others, but in talking about the case we must frame our remarks in a manner that presumes innocence. We must treat the accused in a particular manner.
To return to my opening statement, I may sometimes suspect that academic writing is not so much done to engage peers in argument as it is ventured with the vague hope of avoiding further discussion while dutifully improving one's list of publications. But in writing about academic texts as part of an effort to improve them, I am entitled to presume something that I don't fully believe. Theory makes it possible to present hopes as statements of fact. (Note that the accused is entitled to presume his innocence for the sake of a fair trial even if he is guilty.)
Sorting out what you believe, suspect, hope and fear can begin with defining a set of propositions that serve as presumptions for your research. These are things you can take for granted in setting out to write a text regardless of what you come to believe during the writing or the research that it is about.
The relative durability of systems of presumption (theories) is necessary to keep your style from devolving into a parataxis of cynical judgements or, worse still, a superficial hypotaxis of judgements arbitrarily subordinated "for the sake of argument", albeit an argument one is not interested in having. This happens if you think that all the propositions you write must be "entertained" in the same way, i.e., believed or disbelieved and nothing else. Presumptions allow you to keep your hopes alive even as you learn how the world "really" works. There's always more to learn. And hope is good for your style.
 See J.A. Cuddon's Dictionary of Literary Terms, third edition. London: Penguin. 1991.
 In Philosophy, Rhetoric and the End of Knowledge. Madison: University of Wisconsin Press. 1993, pp. 367ff. (Lawrence Erlbaum Associates has recently published a second edition of this book, reworked by Fuller and Jim Collier as a text book. Worth getting a hold of.)