Wrote about using two spaces.

site/writings/two-spaces.org

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+#+title: Two spaces
+#&summary
+Not one.
+#&
+#+license: wtfpl
+#+startup: showall
+#&toc
+
+
+* Two spaces
+
+When I end a sentence and intend on writing a new, I type two spaces instead of
+one.
+
+I do this only to separate sentence endings from period-terminated
+abbreviations.  Consider this sentence:
+
+: I eat couches, e.g. brown ones. They are nice.
+
+If you didn't know that "e.g." is an abbreviation, you might think that there
+are three sentences: "I eat couches, e.g.", "brown ones.", and "They are nice."
+
+Now consider this sentence:
+
+: I eat couches, e.g. brown ones.  They are nice.
+
+By typing two spaces between the sentences, I have made clear that there are
+only two sentences, and that the period in "e.g." is not the end of a sentence.
+
+The problem is that the period has two purposes: To end a sentence and to end
+some abbreviations.  Always using two spaces to separate sentences solves this.
+
+
+* Other solutions
+
+** Revolution
+
+The best solution would be to use a separate character for abbreviation
+termination, or none at all, so that the period is exclusively used for ending
+sentences.
+
+
+** No change
+
+One might think that another solution is to use just one space, the very thing
+that I'm arguing against.  In the example above with one space between
+sentences, it's actually /not/ difficult to see that there are only two
+sentences: We know that a sentence must start with an uppercase letter, and
+"brown" after "e.g." does not, so it's not a new sentence.
+
+However, uppercase letters *can* occur after abbreviations if they are part of
+given names.  Consider this sentence:
+
+: I eat couches, e.g. Priscilla's brown one. They are nice.
+
+It's not clear that "Priscilla'" does not start a new sentence, because it's very
+similar to "They": Both words start with an uppercase letter and are placed
+after a period and a space.  But "Priscilla's" is just another word in the first
+sentence!
+
+This almost shows that the one-space methodology is insufficient, but not
+completely.  One can argue that if we know all valid abbreviations, we can just
+check if a period is an end to an abbreviation or not, and determine that way
+whether it's a sentence.
+
+But this is only true if the abbreviation can be used in only one way!  Read
+this sentence:
+
+: I used to eat couches bef. I found the cow.
+
+It uses the abbreviation "bef." for "before"; see
+[[http://public.oed.com/how-to-use-the-oed/abbreviations/]].
+
+The sentence can be read in two ways: Either you read it as one sentence -- "I
+used to eat couches before I found the cow" -- or you read it as two sentences
+-- "I used to eat couches before." and "I found the cow."
+
+Both are valid (at least if you accept that a preposition can be the last word
+in a sentence).
+
+I admit that that this example is a bit extreme.  After all, most abbreviations
+can be used only in unambigious ways.  Nevertheless, it still shows that just
+using a single space between sentences *is insufficient*!
+
+Also, we have assumed that all abbreviations are known, which excludes temporary
+(and to some extent field-specific) abbreviations.  This is not good!  It's much
+easier to just use two spaces between your sentences!
+
+
+* Two spaces and fixed width output
+
+Due to my background/foreground as a programmer, I have a tendency to limit
+myself to 80 characters per line, and write two newlines when I start a new
+paragraph (just look at the source of this page).
+
+This is just a choice of representation which works well in many cases, but I
+won't write about that.  The interesting thing is: How does this mix with using
+two spaces between sentences?  This can actually be a problem; look at this
+sentence:
+
+: Bla bla bla bla bef. bla bla.
+
+This is one sentence, as "bef." does not end the sentence.  If we assume that
+the line width is not 80 characters, but instead 16 characters, then the line
+should be wrapped like this:
+
+#+BEGIN_SRC
+Bla bla bla bef.
+bla bla
+#+END_SRC
+
+But now it's not clear if "bef." ends a sentence or not!  If we want to turn the
+fixed-width representation back into a simple line representation, we don't know
+if we should insert one or two spaces after "bef.".  How do we solve that?
+
+The answer is that, when you line-wrap, you don't split word sequences separated
+by ". ", .i.e. you see an abbreviation and its following word as a single word.
+That way, you would end up with:
+
+#+BEGIN_SRC
+Bla bla bla
+bef. bla bla
+#+END_SRC
+
+which would not cause any problems.
+
+
+* General thoughts
+
+Most natural languages have some amount of unambiguity, and part of it seems to
+make some things easier, i.e. allowing speakers to be loose when talking about
+stuff.