The confusion between PSS and PPS comes up whenever someone needs to add a second afterthought to a letter or email. Both look plausible at a glance. Only one is correct. The right abbreviation is PPS, and understanding why takes about thirty seconds.
What PS stands for
PS is short for the Latin post scriptum, meaning "written after." When you write a PS at the bottom of a letter, you're adding a note that comes after the main body of text. The abbreviation is universally accepted in both formal and casual writing, and it functions the same way in English, French, Spanish, and most European languages.
One PS is straightforward. The error arrives with the second one.
Why PPS is correct and PSS is not
When you need a third block of text after your first postscript, the Latin logic extends: post post scriptum, meaning "written after the after-written." That gives you PPS. Each P represents one instance of "post," not a doubling of the S. The S stands for scriptum and stays singular.
PSS doubles the wrong letter. It suggests the S is what multiplies, which would make it something like "post scriptionem scriptionem." That's not a real Latin construction. PSS doesn't appear in any major style guide and isn't endorsed by the Chicago Manual of Style or similar authorities on written English.
The pattern holds consistently: a third postscript would be PPPS. Each additional "post" adds another P to the front.
How the mistake spreads
PSS feels right because English speakers instinctively pluralise by adding letters to the end of a word. We write "SSs" for multiple Social Security numbers, "IDs" for multiple identification cards. Applying that same instinct to PS produces PSS. It's a logical error built on English habits colliding with Latin abbreviation rules.
The mix-up is also reinforced by how rarely people need to write a second postscript. Most writers encounter PPS once every few years. Without frequent exposure, the wrong form sticks just as easily as the right one. This pattern shows up across common spelling errors like "incase" vs "in case", where a spoken habit overrides the written standard.
Quick reference: postscript abbreviations
- PS: first postscript (post scriptum)
- PPS: second postscript (post post scriptum)
- PPPS: third postscript (post post post scriptum)
In practice, a PPPS is a sign the letter needs restructuring. If you're writing three postscripts, the extra information probably belongs in the body.
Does it matter in informal writing?
In a text message or casual email to a friend, nobody will dock points for PSS. Context forgives a lot. But in a business letter, a published piece, or any setting where precision signals professionalism, PSS marks a writer who doesn't know the standard. PPS is a small detail. It's also the kind of small detail that gets noticed by people who know it.
The same principle applies to abbreviations like P.S. with full stops versus PS without. Both are acceptable depending on the style guide your context follows. The PPS vs PSS question, though, isn't a style preference. PPS is right. PSS isn't.
A simple way to remember it
Think of each P as a "post." One P, one "post." Two Ps, two "posts." The S at the end is always just scriptum, always singular. If you can remember that PS means "after-written," PPS as "after-after-written" becomes obvious. That's the same kind of building-block logic that helps with other easily confused pairs, like bought vs brought, where tracing a word back to its root resolves the confusion immediately.
Write PPS. Never PSS. The Latin built it that way, and no style authority has changed it.