Oh, the drama! Oh, the debate! My answer on the subject? It depends. The publishing world is trending towards a single space after periods, yet not all of the academic world is following suit. See below for specifics.
For the Publishing World
The large publishing houses in the United States are using Chicago Manual of Style (CMOS). If you are planning to submit a manuscript (or publish one and look more professional) this is the way to go.
“The view at CMOS is that there is no reason for two spaces after a period in published work…it is inefficient, requiring an extra keystroke for every sentence… So, in our efficient, modern world, I think there is no room for two spaces after a period.” More CMOS FAQs here.
I was trained to use two spaces after periods, but am now retraining myself to use a single space to follow current publishing trends. You can look up other CMOS specifications on the Purdue Owl, as well as, on the CMOS site.
For the Academic World
You can use either, but you need to stay consistent in your paper. Although, before you run along and add in all those double spaces after periods, realize that there is change in the air. According to the Modern Language Handbook:
“Publications in the United States today usually have the same spacing after a punctuation mark as between words on the same line. Since word processors make available the same fonts used by typesetters for printed works, many writers, influenced by the look of typeset publications, now leave only one space after a concluding punctuation mark. In addition, most publishers’ guidelines for preparing electronic manuscripts ask authors to type only the spaces that are to appear in print.
Because it is increasingly common for papers and manuscripts to be prepared with a single space after all punctuation marks, this spacing is shown in the examples in the MLA Handbook and the MLA Style Manual. As a practical matter, however, there is nothing wrong with using two spaces after concluding punctuation marks unless an instructor or editor requests that you do otherwise.” Read more FAQs from the handbook here or see what MLA.org states here.
So, my advice? Start getting used to putting a single space after all punctuation marks. After doing a search on what is trending in the business world, I found that they follow what is set forth by publishers–meaning one space.
This style is keeping with older publishing practices and is retaining the use of two spaces after peiods.
“Regarding punctuation in manuscript drafts, APA suggests using two spaces after periods ending sentences to aid readability.” More info here.
If you are not sure about format in regards to anything academic, my favorite source is The Purdue Owl. They have a site that is easy to navigate.
Some people feel VERY strongly about the spaces after a period. I am not trying to insult one party or the other–simply to inform. I personally like two spaces after a closing punctuation mark, but I have learned to adapt. Why? I think it is easier to see the end of the sentence. I read a lot of papers, so readability is key. Though, in the scope of the universe, it doesn’t matter that much–just be consistent.
What is your preference?