The abbreviation traces back to Rome. In antiquity, correspondence was etched onto wax tablets or inked across expensive parchment. The physical mechanics of letter writing etiquette left zero margin for editorial revision. Once the ink dried on post scriptum, Latin for "written after", an omitted detail could not simply be inserted into paragraph two without damaging the medium or ruining the layout.
Scribes needed an accepted convention to signal that late-breaking news or a forgotten instruction was deliberately appended after the formal sign-off. The formula was simple: sign your name, add the initials, write the additional thought, and seal the scroll.
For centuries, handwritten notes retained this functional necessity. Nineteenth-century love letters and military dispatches alike leaned on the postscript to deliver sudden declarations or operational updates. The arrival of typewriters in the late 1800s cemented the habit. Striking a mechanical ribbon against paper created permanent impressions; retyping three pages because of an overlooked meeting time was out of the question. The postscript remained an indispensable mechanical escape hatch until screen-based text processing rendered it technically obsolete in the late twentieth century.
