Originating from the Latin dies (day) and diarium (daily portion), one of the oldest-known diaries was kept by Roman Emperor Marcus Aurelius, followed by several travel and day-to-day journals of Eastern Asia, then those of Middle Eastern origin. Diarists began to focus more on the emotions and human experience in Medieval days until, after the Renaissance, when even greater emphasis was placed upon recording opinion, desire and expectations, as well as personal insight and emotions.
While a diary might later support research done for a biography, a a historian's accounting of an era, or to recollect details of a life's era for a memoir or autobiography, the diary is written, at least initially, without an eye to eventual publication. (After all, could the diarist be as open, as vulnerable on the page if he or she wrote with the intention of having others read the diary's pages later? Likely not, arguably.)
Some evidence suggests some notable diaries are written with the express purpose of seeing a one-day publication, generally to have a final word, real or fabricated, of one's life or career, often posthumously. (British playwright and memoirist Simon Gray is one example who springs to mind of one who fell under such scrutiny.)
Diaries written with eventual publication in mind aside, what is the purpose, then, of keeping a diary for one's own use? Writing one's thoughts and emotional states causes the writer to process their details and sort life's information in a (presumably) healthy and constructive way. Yes. True. But, is there a greater conversation to be had in that the diarist ultimately aims to set record of his or her existence?
This notion, one could argue, is supported boldly in "The Diary of a Young Girl" by Anne Frank, who wrote while in hiding in Nazi-occupied Amsterdam. Surely Frank, even at her young age understood the dangers of the day and feared her own obliteration, even if subconsciously.
That said, even Anne Frank's diaries have fallen to speculation of genre in recent years in Francine Prose's "Anne Frank: The Book, The Life, The Afterlife" in which Prose suggests “Anne Frank thought of herself as not merely a girl who was keeping a diary, but as a writer,” and pins responsibility on Frank herself, first at 13, then at 15, and finally on Frank's father Otto, who edited and published his daughters journals after the conclusion of WWII.
Is it possible to write just to write, with the intention of keeping the words secret forever? Or, does the act of recording a thought, en emotion, a perception of an event, carry with it the implication of a desire of permanence?
I'm inclined to say: yes, while writing one's thoughts and emotions does offer a certain clarity (and a great deal of entertainment when re-read later), some kernel of self must surely aim for a given moment to last forever when we record the details of ourselves.
That said, may the diaries of my own teenage years never, ever be discovered.
Further reading: 6 diaries to read right now