TeX (and LaTeX) defaults to English spacing, but you can switch to French spacing using the declaration:
and switch back again using
There was no en-space on a typewriter, so typists started using two spaces in an attempt to emulate that slightly larger than one space look. This habit has spread to word-processor users as well, and now many people incorrectly assume English spacing means adding two spaces after a full stop, which is too wide and looks ugly, but this error shouldn't be used as a criticism against English spacing.
There has been a gradual trend towards French spacing over the last century, and some publishers insist on it. I think this may in part be due to a backlash against the ugliness of two spaces in typewritten and word-processed documents. In fact the Oxford Style Manual  simply states, “In text, only use a single space after all sentence punctuation.”
Personally, I prefer English spacing, particularly in reference books. I have many reference books on my shelf, but I haven't read any of them from cover-to-cover. I flick to a particular section and skim through the paragraphs until I reach the desired bit of information. Sometimes I've already looked something up, so I have a vague idea as to where to find the information. The extra space between sentences makes it easier to locate a particular sentence.
This isn't so much of an issue with books designed to be read from beginning to end, such as a novel. However, I have read one such book that used a font where the commas had tiny tails and most of the sentences contained multiple proper nouns, which made it very difficult to read as it wasn't clear where the sentences ended. Is that a full stop followed by a new sentence that happens to start with a proper noun, or is it a comma whose tiny tail is blurred by my short-sighted eyes followed by a clause that happens to start with a proper noun? A well-written, well-presented document should not interrupt the reader, forcing them to continually go back to re-parse a sentence.
However, if you are writing a document, whether prose or technical, with the intention of having it published you must check with the publisher's guidelines to see if they insist on a particular style.
- If an end of sentence punctuation mark follows a lower case
character, TeX assumes the punctuation mark indicates the end of
the sentence. For example, as in:
Did you see that? I certainly did.
- Where this isn't the case, use \␣ (backslash
followed by a space).
This can happen when a sentence contains a lower case abbreviation, e.g.\␣like this one.
- If an end of sentence punctuation mark follows an upper case
character, TeX assumes the sentence hasn't ended at that point.
For example, as in:
The G.P. said it was only hypochondria.
- Where the sentence actually ends with an upper case letter,
add \@ after the letter and before the punctuation mark.
Yesterday, I saw my G.P\@. Tomorrow I'm going to see the specialist.
Note on Typewriter Fonts
\nonfrenchspacing in a monospaced font will insert
two spaces between sentences, emulating a typewritten document.
This book is also available as A4 PDF or 12.8cm x 9.6cm PDF or paperback (ISBN 978-1-909440-00-5).