The apostrophe has emerged as the punctuation mark, which causes most problems for Britons, according to a new survey.
The survey of nearly 2,000 UK adults revealed that almost half were unable to use the apostrophe properly.
The most common mistake was not knowing how to punctuate a possessive plural.
The test, set by the SpinVox speech technology company, revealed that 46 percent of those who sat it thought that, in the context set, "people's choice" was wrong - whereas it is correct.
The adults were also asked which mistake most annoyed good punctuators.
Replacement of "they're" with "their" was the most irritating, followed by the use of an apostrophe to denote a plural - as in the use of the incorrect "boy's" instead of correct "boys''."
Joint third was using "its" instead of "it's" and "it's" instead of "its" - the confusion between a plural possessive and abbreviation of the phrase "it is".
"The problems people have with apostrophes arise from the hopeless state of English punctuation and spelling," the Telegraph quoted Professor Christopher Mulvey from the Museum of the English Language at Winchester University, one of Britain''s foremost English language experts, as saying.
"The situation is so confusing that people panic and hypercorrect. To get it right, you need to look up the rules every time you think an apostrophe might be needed - and do this for the next six months in order to ''internalise'' the rules," he added.