Austin Ziegler wrote:
> On 11/30/05, Jeffrey Schwab <jeff / schwabcenter.com> wrote:
> 
>>Austin Ziegler wrote:
>>
>>>On 11/29/05, Kevin Olbrich <kevin.olbrich / duke.edu> wrote:
>>>
>>>>Depending on the text you might be able to search for a period (or other
>>>>punctuation) followed by two spaces.  It's not robust, but if you know that
>>>>convention will be followed by the authors, then it can work.
>>>
>>>That, in fact, is a very *bad* metric to follow, as the proper spacing
>>>after sentence punctuation is a single space. The only reason that two
>>>spaces was used in the past is the space used between sentence endings
>>>in typeset work is a little wider than that used between words (an
>>>em-space vs. an en-space).
>>
>>Not true at all.  I was always taught to use double spaces after
>>sentences in grade-school homework assignments done on plain word
>>processors or typewriters.
> 
> 
> Then, quite honestly, you were taught wrong. I was taught to use
> double spaces with a typewriter or when using fixed-pitch fonts
> (although that was later, since most computers and printers didn't
> have reliable kerning routines until I was out of university).
> Ultimately, the use of double spaces after a period is wrong *even
> with fixed-pitch fonts*, but it was done to be clearer since the width
> of the em-space and an en-space on a typewriter with a Courier-like
> font is exactly the same. The two spaces *simulates* an em-space in a
> typeset piece of work. (And that is *fact*, not opinion.)

The Bedford Handbook, which has been my bible for writing conventions 
through the past ten years, lists two sets of guidelines:  Those 
recommended by the Modern Language Association (MLA), and those 
recommended by the American Psychological Association (APA).  It says 
that the MLA style is typically taught in English classes, but that the 
APA style is common in the social sciences.  Here is the explanation of 
the MLA guidelines, from page 633 of the Bedford Handbook for Writers, 
(c) 1994:


MLA Guidelines [for essays]:

	In typing the text of the essay, leave one space after words, commas, 
colons, and semicolons and between the dots in ellipsis marks.  Leave 
two spaces after periods, question marks, and exclamation points.
	To form a dash, type two hyphens with no space between them.  Do not 
put a space on either side of a dash.


The Handbook goes on to say (p. 635):


	Although the APA guidelines call for one space after all punctuation, 
most college professors prefer two spaces at the end of a sentence.  Use 
one space after all other punctuation.
	Although two spaces are used after a period that ends a sentence, use 
only one space after a period that follows a person's initial (B.F. 
Skinner).
	To form a dash, type two hyphens with no space between them.  Do not 
put a space on either side of a dash.


The Handbook itself uses only single spaces at the ends of sentences. 
Still, I hardly think there is one conclusively "right" or "wrong" 
convention.  Until I am convinced otherwise, I will continue to use two 
spaces to separate sentences.  This makes sentences easier to lex with 
regular expressions, and makes them stand out to text editors and human 
readers.