[Clue: he was born three weeks ago, on 23 September 2014.]
Originally, as I understand it, the word birthday meant the day of one's birth. It was a one-off event.
I don't want to quarrel with the idea of extending this to cover anniversaries of one's birth. I'm comfortable saying that I've had forty birthdays, or thereabouts.
I'm not sure how far back the concept of celebrating the anniversary of one's birth goes, but it at least pre-dates Moses (Genesis 40:20), and therefore long pre-dates the English word birthday. This isn't a question about how that custom arose, but about the way we use the English word birthday and whether it makes sense. Does it refer to the day of one's birth, or an anniversary, or both?
Convention seems to dictate that my son's first birthday is when he's a year old; his second birthday will be when he's made it through another year; and so on. Now this is odd: if his first birthday is in a year's time, what's become of the day of his birth? Is this now considered not to be a birthday at all? I'd have expected him to become a year old on his second birthday, and so on.
In summary, the language drift seems to have gone like this:
- notion of birthday = the day of one's birth;
- notion of birthday extended to include anniversaries;
- notion of birthday now restricted to exclude the day of one's birth.
Is this a bit weird, or what? Has it just happened so that the cardinals (four years old) line up with the ordinals (fourth birthday)?
Is it because birthday is now shorthand for anniversary of one's birth?
Am I missing something?