Next: \frenchspacing & \nonfrenchspacing, Previous: \spacefactor command: Assigning an explicit space factor, Up: \spacefactor: Extra space after punctuation   [Contents][Index]

19.7.3 \@ ¶

Synopsis:

capital-letter\@. (sentence ends with capital letter)
lowercase-letter.\@ more...  (sentence continues after period)

Treat a following period (or other punctuation) as sentence-ending, and a preceding punctuation mark as non-sentence-ending.

By default, LaTeX thinks that a period ends an abbreviation if the period comes after a capital letter, and otherwise thinks the period ends the sentence.

This example shows both of the common cases:

The songs \textit{Red Guitar}, etc.\@ are by Loudon Wainwright~III\@.

The first period ends the abbreviation ‘etc.’ but not the sentence, so we put \@ after it. The second period ends the sentence; since it’s preceded by a capital letter, we put \@ before it.

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 text modes. If you use it outside of a text mode then you get the error ‘You can't use `\spacefactor' in vertical mode’ (see Modes).

All the above applies equally to question marks and exclamation points as periods, since all are sentence-ending punctuation, and LaTeX increases the space after each in the same way, when they end a sentence. LaTeX also increases spacing, to a lesser extent, after colons, semicolons, and commas (see Space factor description).

In contrast: the converse case is a period (or other punctuation) that does not end a sentence, in a context where LaTeX thinks it does. For that case, follow the period with \@, or, usually (as we will see in the following sections), a backslash-space (\ see Backslash-space: ‘\ ’) or a tie (~, see ~, \nobreakspace). Another example:

Good stuff (hay, straw, etc.\@) is for sale at Rancho PQR\@.

Here again, the \@ comes after the period in the middle of the sentence (and before the closing parenthesis), but before the period that does end the sentence after a capital letter.

All that the command \@ in fact does is set the current \spacefactor value to 1000. This has all the desired effects, due to the rules described (and those left undescribed) above.