I have recently been doing a lot of collaborative writing, and so have come face to face with the differences between my own and other people's grammatical habits. Two of them in particular are interesting to me.

Two spaces after a period

I use only one space at the end of a sentence, and ritually replace two spacers when I find them. Why do they exist at all? I think they break up the flow of the line and I constantly confuse them with two space typos of the kind that come between words in a sentence.

monospacingIt turns out that the origin of the two space is a holdover from the typewriter. Typewriter fonts are generally monospaced – the same amount of space exists between each letter – and so two spaces after the period helped to mark off one sentence from the next. Since about 1982, however, fonts have almost entirely been proportionately spaced, so putting two spaces after the period just doesn't make sense anymore (if it ever did).

Commas before the last item in a list

I always put a comma before the last item in a list, whereas many folks don't. This would not be a big deal except that the lack of a convention can lead to a lot of confusion. This is especially true in sentences where each list item is a long phrase – a phenomenon that pops up waaaay too much in academic writing. But it's a problem even in simple sentences. Here's an example of a sentence that foregoes a comma at the end of the list at the expense of comprehension:

Jaime invited us over for a party and we brought maple syrup, Sunkist, crackers and cheese.

Now, if we're culinarily picky, we might want to know if Jaime is bringing some crackers and also some cheese, or if he's bringing a tray of crackers and cheese. Okay, not the best example. But the point remains – as long as we don't know whether the author likes to put commas before the last list item, we don't know which thing Jaime is bringing.

Here's another example:

I've managed to teach my dog to fetch, speak, shake hands, roll over and play dead.

Are those two separate tricks there at the end? We need to know, damnit!!