Holiday names and apostrophes confuse me. For instance, is it Mothers Day or Mother's Day or Mothers' Day?
- If we think of it as a day to celebrate mothers, or a day in which mothers are the theme, then we would use the adjectival form and say Mothers Day. This would be a similar concept to Independence Day, Memorial Day, or Thanksgiving Day.
- If we think of it as a day belonging to one particular mother (presumably mine), we would use the singular possessive and call it Mother's Day. This would be like Someone's Birthday.
- If we think of it as a day belonging to all mothers, then we would use the plural possessive and call it Mothers' Day. This would be like the twins' or the octuplets' birthday.
I like the first and third options, but I can never decide which I prefer. Whichever we use, though, we ought to be consistent and apply the same apostrophe pattern to holidays like Fathers(') Day, Veterans(') Day, All Saints(') Day, and Grandparents(') Day.
This brings us to February 14. As Eerongal pointed out, the original name was St. Valentine's Day - so, etymologically speaking, the singular possessive form seems correct even when the St. part is dropped. However, I might argue that either of the other forms could also be correct, if you think of the word valentine as having evolved to mean "special someone". In this sense, the holiday can be seen as either celebrating or belonging to those special people in our lives whom we love - so it could be Valentines Day or Valentines' Day.