You know what an essay is. It's that piece you had to write in school, hopefully not (but probably) the night before it was due, about a subject such as What Freedom Means to You—at least five pages, double-spaced, and don't even try to get away with anything larger than a 12-point font. (Kudos for thinking to tweak the margins, though.)
Remember the difference and get an 'A' for effort.
You might also know that essay can be a verb, with its most common meaning being "to try, attempt, or undertake":
A very close approach to the evil of Idi Amin is essayed in Giles Foden's 1998 novel The Last King of Scotland, whose narrator is the Scottish personal physician to the dictator.
— Norman Rush, The New York Review of Books, 7 Oct. 2004
The principal accidents she remembers, before last summer's, involved chipping a couple of teeth while, as a fifth grader, she was essaying a back flip off a diving board,...
— E. J. Kahn, Jr., The New Yorker, 17 Aug. 1987
The verb assay, meanwhile, is used to mean "to test or evaluate" and can be applied to anything from laboratory samples to contest entries:
He bounced from job to job, working on a shrimp boat and later for Pan American Laboratories assaying chemicals coming in from Mexico.
— Steve Clark, The Brownville Herald, 21 Apr. 2017
"Each burger will be assayed by visitors and a panel of judges, including local chefs Jen Knox, Gina Sansonia, Judith Able, Bret Hauser, Camilo Cuartas and Peter Farrand."
— Phillip Valys, SouthFlorida.com, 19 May 2017
While this distinction might seem clear-cut on the surface, there exists a great deal of historical overlap between essay and assay. The two words derive from the same root—the Middle French essai, which ultimately derives from a Late Latin noun, exagium, meaning "act of weighing."
At one time, assay and essay were synonyms, sharing the meaning "try" or "attempt." In the 17th century, an essay was an effort to test or prove something:
Edmond: I hope, for my brother's justification, he wrote this but as an essay or taste of my virtue.
— William Shakespeare, King Lear, 1606
For the modern noun use of essay to mean "a written exploration of a topic," we can almost certainly thank Michel de Montaigne (1533-1592), a French writer noted for working in the form. Borrowing a word that emphasized their identity as literary "attempts," Montaigne devised Essais as a title for the vignette-typed pieces that he began publishing in 1580 and spanned over a thousand pages, covering subjects as varied and wide-ranging as solitude, cannibalism, and drunkenness.
Those last ones probably won't be in the final exam.
Date published January 15, 2015 by Shane Bryson. Date updated: September 17, 2015
Barring the obvious answer (to get a degree), in answering this question we need first to ask, what distinguishes an essay from any other form of writing? Most people will have strong intuitions that newspaper articles, scientific reports, and short stories, for example, are not forms of essay, but it might be hard to distinguish exactly why these don’t count as essays.
The difference lies in the stance a writer takes in composing an essay and the kind of thing that an essayist tries to do. We find a clue to the distinction in the general definition of the word “essay”: as a verb it means “to try,” and my dictionary of literary terms calls its noun form “a composition having no pretensions to completeness or thoroughness of treatment” and says that the “chief implication of the term is ‘a tentative study.’”
Essays try to provide an understanding of things that are essentially matters of interpretation, where the prospect of the final word on a subject is remote. In contrast, scientific reports try to describe something that happened (an experiment), and they are supposed to be minimally interpretive and nearly indisputable. Newspaper articles are similar in this way, presenting the facts and just the facts (at least in theory).
But something else must distinguish the essay form, since fictional narratives such as short stories also in some ways present a tentative study of things,. These two forms usually differ in content and aim. Narratives tell stories about how events unfold for characters and usually try to make us feel a certain way. Essays are closer to scientific reports in that their purpose is to tell us, most often explicitly, about the way we ought to understand something.
In sum, whereas a scientific report aspires to be indisputable, an essay strives to give a convincing interpretation of something (and interpretation is by definition disputable). Whereas a short story aims to make us feel, an essay intends to make us think.
Finally, a scientist is supposed to be inessential to her experiment and report; anyone should be able to perform the experiments, get the results, and record them in much the same way. A fiction writer relates to her writing in the opposite way; the story is fundamentally changed when told by anyone else. The essayist, again, falls somewhere between these two extremes. An essay’s argument should be convincing no matter who authors it—the logic of the argument should stand independent of the author—but an essay is also always an expression of the essayist’s opinion, which is by definition not objective fact.
In short, the essayist writes to communicate her opinion on a subject in order to convince her audience to take up this opinion. This is what makes an essay.
Academic essays, in particular, are characterised by a certain standard and approach.
essay. 1960. In S. Barnet, M. Berman, & W. Burto (Eds.), A dictionary of literary terms (pp. 39-40). Toronto, ON: Little, Brown.
Overview of academic essays