\@
Synopsis:
capital-letter\@.
Treat a period as sentence-ending, where LaTeX would otherwise think
it is part of an abbreviation. LaTeX thinks that a period ends an
abbreviation if the period comes after a capital letter, and otherwise
thinks the period ends the sentence. By default, in justifying a line
LaTeX adjusts the space after a sentence-ending period (or a question
mark, exclamation point, comma, or colon) more than it adjusts the space
between words (see \spacefactor
).
This example shows the two cases to remember.
The songs \textit{Red Guitar}, etc.\ are by Loudon Wainwright~III\@.
The second period ends the sentence, despite that it is preceded by a
capital. We tell LaTeX that it ends the sentence by putting
\@
before it. The first period ends the abbreviation
‘etc.’ but not the sentence. The backslash-space, \
,
produces a mid-sentence space.
So: if you have a capital letter followed by a period that ends the
sentence, then put \@
before the period. This holds even if
there is an intervening right parenthesis or bracket, or right single or
double quote, because the spacing effect of that period carries through
those characters. For example, this
Use the \textit{Instructional Practices Guide}, (a book by the MAA)\@.
will have correct inter-sentence spacing after the period.
The \@
command is only for a text mode. If you use it outside of
a text mode then you get ‘You can't use `\spacefactor' in vertical
mode’ (see Modes).
Comment: the converse case is a period ending an abbreviation whose last
letter is not a capital letter, and that abbreviation is not the last
word in the sentence. For that case follow the period with a
backslash-space, (\
), or a tie, (~
), or \@
.
Examples are Nat.\ Acad.\ Science
, and Mr.~Bean
, and
(manure, etc.\@) for sale
(note in the last one that the
\@
comes before the closing parenthesis).