Madame de Sévigné, writing to her daughter on 5 February 1671, ended a long, polished letter, signed it, folded it, and then added a postscript of nineteen words. The postscript reads, in English: I have not said anything I meant to say. I will write again on Friday.
She did not write again on Friday. She wrote on Sunday. The Sunday letter is longer and less interesting than Wednesday's postscript.
The postscript is one of the few literary forms invented by accident. It exists because the writer has finished a letter and then thought of something more. Its etymology is plain: post scriptum, after the writing. Its function, however, is not.
A postscript is not a continuation. A continuation would be the next paragraph. A postscript happens after a signature, which is to say, after the writer has, with some ceremony, declared herself finished. The PS is the second voice of the same person, speaking in a slightly different register because the formal one has been closed.
The form is older than the personal letter as we know it. Cicero used postscripts. Saint Paul, in Galatians, points out the size of his own handwriting in what is functionally a postscript. The early modern English letter writers used them constantly. Samuel Johnson sometimes wrote postscripts that exceeded the body of the letter in length and were noticeably more candid.
Why? The body of a letter is an act of composition. The signature is the end of that act. The postscript is what falls out, when the composition is over.
The candour of the postscript is not always sincere. Some writers have used it strategically. Lord Chesterfield, in letters to his son, sometimes placed the actual instruction in the postscript, where it would land more heavily for having been omitted from the body.
But there is something to the general rule: when one writes a postscript, one's guard is down a little, because one has already, in one's own head, finished. The defences come down with the pen lifted.
Letter manuals, of which there were many in the nineteenth century, took different views. The 1851 Hill's Manual of Social and Business Forms, which a generation of American clerks studied at evening school, recommends against postscripts on grounds of carelessness. A well-composed letter, the manual insists, should not require an afterthought.
By 1922, Emily Post had softened. She permitted postscripts but warned against their use in formal correspondence, particularly invitations.
By 1970, in a small handbook on letter writing published by Faber, the British essayist Mollie Panter-Downes defended the postscript outright. She argued that the most truthful sentence in any personal letter she had ever received had been a postscript.
The argument can be made empirically. If one reads a collection of any prolific letter writer — Henry James, Elizabeth Bishop, Iris Murdoch — and pays attention only to postscripts, one finds that the postscripts tell a different story than the bodies of the letters do.
James's postscripts are gossipy. Bishop's are often about money or weather. Murdoch's, late in life, sometimes ask the recipient to write back, in a register the body of her letters did not permit.
The form did not survive the transition to email intact. Email permits revision; one can edit the body before sending, which removes the architectural reason for the postscript. The sign-off and the signature can be moved. The first draft is the final draft.
Some habitual letter writers have continued the practice anyway. The poet Kay Ryan, in published email correspondence with her editor, sometimes used a PS even in email, treating it as a deliberate formal choice rather than an accident of composition.
The PS in that case becomes affectation. It is still useful, but it is no longer honest.
There is another kind of postscript, harder to recover, which is the marginal note. The writer who has finished, folded, and addressed an envelope, then opens it to add a line in different ink on the back of the second page, or across the top of the first.
These are very hard to anthologize, because they require facsimile reproduction. They are also some of the best sentences in the history of personal letters, because they were written in the most informal posture a writer can adopt: standing up, having decided not to be done.
The case for the postscript is, finally, a case for not finishing. Many of us write — letters, books, reviews — under the illusion that finishing is the point. We compose toward an ending. The postscript suggests that the ending is not always where the writing finds itself.
Sometimes the truer sentence is the one that comes after.
Madame de Sévigné's Sunday letter, when she finally wrote it, ended without a postscript. We are entitled to think a little less of it.