Whether you’re talking about the passcode associated with your debit card or the number that is linked to any number of other kinds of accounts, a PIN is a personal identification number. It’s an acronym that has become an accepted word of its own. When we see PIN in print, we are more likely to say “pin” than we are to say the individual letters “pee-eye-enn.” That much is fine and perfectly acceptable.
However, by referring to the series of digits as a PIN number, you are being completely and utterly redundant. PIN stands for “personal identification number” and, as such, PIN number would then expand to “personal identification number number.” That’s pretty silly, right? Then why does the official website of the Vancouver Public Library even make this mistake?
The same concept applies to other related acronyms like SIN (social insurance number), SSN (social security number), and TIN (taxpayer identification number). You should never say SIN number or SSN number, because you would be making the same mistake as you would saying SIN number. It’s not a matter of writing style; it’s just grammatically incorrect.
Granted, some redundancy is good under certain circumstances, but the redundancy of PIN number is simply unacceptable. Whenever you use any kind of acronym, try replacing the acronym with the full words to ensure that your sentence still makes grammatical sense.
Do you have a suggestion for a future Grammar 101 post? Let me know through the comment form below.