Rhetoric and Disciplinarity: Rhetoric, understood as the study and mastery of interpretation and argument, is an interdisciplinary art, which means that certain modes and strategies of interpretation and argument can be applied regardless of the discipline in which one is working. At the same time, there are also always discipline-specific modes and strategies of interpretation and argument that apply.

Writing in a Discipline: When we talk about writing across the disciplines, we are seeking an awareness of the features of writing that apply universally and those that will change depending upon the discipline in play. As such, regardless of the discipline, it is universally true that, when writing in a certain discipline, you should familiarize yourself with the assumptions, commitments, motives, and conventions of that discipline.

Writing Across the Disciplines: What is universally necessary for all academic writing? What things can we say must appear in a given piece of academic writing? 

The Elements Across the Disciplines: By my count, seven elements - evidence, analysis, question/problem, method, argument, structure, and implications - appear in all academic writing across the disciplines. Sometimes the same element will appear very differently in different disciplines, and sometimes those different disciplines will introduce new elements. 

Evidence: First of all, academic writing begins with evidence. That may sound obvious or commonsensical, but what, really, is evidence? The word comes from the Latin video, "to see," which means that evidence is perceptible, able to be seen. In academic writing, it is not enough to have facts, information, logic, and so forth that supports one's position. That material must be visible, perceptible, able to be seen in the actual paper. Whether one is presenting facts and dates or quotations and summaries, evidence must be literally evident in academic writing regardless of the discipline – this in contrast to, say, some kinds of journalism in which sources are confidential or some kinds of editorials in which a position can be advocated without a thorough presentation of the evidence for it.

Analysis: Evidence always needs analysis. Evidence, in and of itself, does not make academic writing. Regardless of the discipline, academic writing involves the elucidation of evidence in ways that are informed by the assumptions, motives, commitments, and conventions of a discipline. In other words, it is universally true that any instance of academic writing is situated within and committed to a discipline, but what changes, obviously, is the disciplinary commitment of any given piece of writing. It is not a distinction that holds absolutely, but the humanities tend to deal in qualitative analysis while the sciences often deal in quantitative analysis, and the social sciences in both. Qualitative analysis is geared toward the description of things (of qualities), while quantitative analysis toward the measurement of things (of quantities). As such, the humanities attempt to explain the world primarily through the use of language, and the sciences attempt to explain the world primarily through the use of numbers. This is certainly not to say that there are no concepts in the sciences or numbers in the humanities, but there is a significant and meaningful difference in the procedural foundation of these schools of thought. Why is this so? Because the humanities are addressed to subjective experience with the world in which we live, the sciences to the objective reality of that world, and the social sciences to the objective reality of subjective experience.

Question or Problem: In theory, though certainly not in practice, all academic writing needs to be written because it provides us with a better understanding of our world. All academic writing responds to a specific problem or question. The distinction (once more) isn't absolute, but the humanities tend to respond to "problems" on the order of "How should we understand X?"; the sciences often deal in "questions" that can be boiled down to "Is X true or not?" In other words, the humanities help us think about things with which we are already familiar while the sciences give us new information that we don't already have. 

Method: In light of the different modes of analysis across the disciplines, we can say that all academic writing employs a deliberate method that is drawn from a distinct discipline or combination of disciplines. The methods of interpretation and argumentation can and do change from discipline to discipline, but a rigorous method must exist for writing to be properly academic.

Structure: Similarly, all academic writng has structure to it (admittedly, sometimes not as clear as it could be). Like method, structure depends upon the discipline in play: different disciplines use different structures. Yet again these conventions are not absolute, but often the humanities use an Introduction-Body-Conclusion structure, while the sciences use an Introduction-Method-Results-Discussion structure. 

Argument: All academic writing also has an argument - a series of demonstrated claims that add up to a consequential idea - though not necessarily a thesis statement. A thesis is a proposition presented early in an essay that is then supported with evidence and analysis throughout the rest of the essay. Papers in the humanities have theses, but papers in the sciences tend to have hypotheses. A hypothesis is a prediction in response to a question that requires research; that research may prove the hypothesis true (as expected) or untrue (leading to a different answer to the question at hand).

Implications: All academic writing has implications, or extractable knowledge that matters beyond the specifics of the argument. Implications could consist of additional questions that need to be asked, further research that needs to be done, theorizations, speculations, policy implications, or any other strategies that move a discussion beyond the interpretation of the specific issue at hand in an essay.