Question

LaTeX tries to guess whether a period ends a sentence, in which case it puts extra space after it.
Here are two examples where it guesses wrong:

I watched Superman III. Then I went home. 

(Too little space after “Superman III.”.)

After brushing teeth etc. I went to bed.

(Too much space after “etc.”.)

Note that it doesn’t matter how much whitespace you use in the LaTeX source since LaTeX ignores that.

Answer 1

I found the answer here: http://john.regehr.org/latex/. Excerpt:

When a non-sentence-ending period is to be followed by a space, the space must be an explicit blank.
So the second example should be:

After brushing teeth etc.\ I went to bed.

The converse of this problem happens when a capital letter precedes a sentence-ending period in the input, as in the first example.
In this case LaTeX assumes that the period terminates an abbreviation and follows it with inter-word space rather than inter-sentence space.
The fix is to put “\@” before the period.
So the first example should be

I watched Superman III\@. Then I went home.

A handy way to find this error is:

grep '[A-Z]\.' *.tex