It’s an epidemic of obsolete style that we’ve been running into a lot. Somehow the old rule that we should put two spaces after every period has survived well into the 2010’s. We suppose it’s a testament to the force of cultural habit, as the practical reasons for this rule’s implementation have long since disappeared.
Writers used to do this because typewriters used a monospaced font, which gave equal space to all letters. M’s would take up as much as space as i’s. They adopted the double spaces after periods to make it easier for the eye to spot sentence breaks. Fonts these days, however, are proportionally spaced, meaning that the extra space after periods is superfluous. Single spaces are now the formally correct way to do it, according to the Chicago Manual of Style.
Some may argue that they do it for aesthetic reasons, which is fair. For our part, it’s an eyesore. It makes a text look perforated and disjointed. But for personal things, that’s your prerogative.
A friend of ours saw it as a way to add “cheap volume” to an essay. We can’t argue with that. Most professors and GSI’s probably won’t ding you for it. But if you want to do something in a professional capacity, we advise you to stick with the efficient and stylistically correct single space.
For the rest of the double-spacers, it’s simply habit. It used to be the case that teachers and professors would you grade you down for not using two spaces. There might even be some teachers that still do it – and that is the interesting aspect of this phenomenon. This now superfluous and erroneous rule persists, just like the rule (that you’ve undoubtedly heard) that prepositions are incorrect words to end sentences with. That rule is dead, use as many terminal prepositions as you wish to tack on. It’s the same for beginning a sentence with a conjunction, perfectly fine. Yet cultural habits perpetuate. Tradition and habits seem to be imposed for their own sake.
We suppose it is true that we are creatures of habit. Still, this habit is one that our fastidious, OCD sensibilities would like to see obliterated.