2.3.1 Simple commands

Simple commands are just the command name on its own, after the backslash, for example:

\tableofcontents

This example is an instruction to LATEX to insert the Table of Contents at that point. You would usually use this in a book or report (or perhaps a very long article) somewhere close to the beginning, normally after the title page but before the Preface or Introduction. You don't have to do anything else. Provided that you have used the sectioning commands described in section 3.5, all the formatting and numbering for the Table of Contents is completely automatic.

\sffamily\bfseries\Large

These are some more simple command examples: the first switches to the current sans-serif typeface, the second invokes bold type, and the third makes the type the Large size (see section 8.2 for the exact details). In this case, the font changes affect all text after this point: to restrict it, there is a technique called ‘grouping’ (see the panel ‘Grouping’ in section 8.2.2).

Simple one-word commands like \tableofcontents must be separated from any following text with white-space. This means a normal space, or a newline (linebreak) or a TAB character. For example either of these two forms will work:

\tableofcontents     Thanks to Aunt Mabel for all her 
help with this book.

\tableofcontents 
Thanks to Aunt Mabel for all her help with this book.

If you forget the white-space, as in the following example, LATEX will treat everything up to the next space as a command, and end up with what it thinks is a command called \tableofcontentsThanks. There's no such command, of course, so LATEX will complain by displaying an error message (see section 4.2.3.2).

\tableofcontentsThanks to Aunt Mabel for all her help 
with this book.

LATEX swallows any white-space which follows a command ending in a letter. It does this automatically, so you don't get unwanted extra space in your typeset output, but it does mean that any simple command which ends in a letter and has no arguments in curly braces (see below) must be followed by white-space before normal text starts again, to keep it separate from the text.

2.3.2 Commands with arguments

Many LATEX commands are followed by one or more arguments, meaning information to be acted upon. Here are two examples, a chapter title (see section 3.5) and a cross-reference label (see section 7.4.1):

\chapter{Poetic Form}
\label{pform}
The shape of poetry when written or printed 
distinguishes it from prose.

Such arguments always go in {curly braces} like those shown above. Be careful not to confuse the curly braces on your keyboard with (round) parentheses, [square] brackets, or 〈angle〉 brackets. They are all different and they mean different things.

With commands that take arguments you do not need to use extra white-space after the command, because the argument in curly braces will keep it separate from any normal text which comes after it. The following example is therefore exactly equivalent to the earlier one above.

\chapter{Poetic Form}\label{pform}The shape of poetry 
when written or printed distinguishes it from prose.

2.3.3 White-space in LATEX

In LATEX documents, all multiple spaces and TAB characters are treated as if they were a single space during typesetting. All multiple newlines (linebreaks) are treated as if they were a single newline. LATEX does its own spacing and alignment using the commands you give it and the layout in the stylesheet, so you have extremely precise control. You are therefore free to use extra white-space in your editor for optical ease and convenience when editing.

The following is therefore exactly equivalent to the examples in the preceding section (although unusual!):

\chapter        {Poetic 
          Form}                      \label
            {pform}

The shape of           poetry when written or printed 
distinguishes it from              prose.

That is, it will get typeset exactly the same. Try it.

Why would you want odd spacing (or none)? The answer is usually never, but a lot of LATEX is created by computer programs from other systems such as web scripts, XML documents, or databases, and it makes life easier if you don't have to worry about the odd space or two creeping in here and there in normal text: it simply won't have any effect. It also means that you don't have to worry about extra linebreaks between sections or paragraphs, or tabbing in lists of items if you want to use them to make your text easier to edit.

2.4.1 Using the special characters

We have already seen (the first paragraph in section 2.3) how to use the backslash to start a command, and curly braces to delimit an argument. The remaining special characters are:

$

This has a special mathematical meaning in TEX, so if you want to print $35.99 you must type \$35.99

%

The comment character makes LATEX ignore the remainder of the line in your document, so you can see it in your editor, but it will never get typeset. For example:

Today's price per kilo is €22.70
% get Mike to update this daily

If you want to print 45% you must type 45\%.

As with all comments in documents, whether LATEX or just a wordprocessor, don't forget to remove them before sending the original document source to someone else!

and must never be allowed authority to create a 
charge on the department again. 
% and fire those idiots down in Finance!

^

The caret sign in mathematics lets you type \(E=mc^2\) to get E=mc². If you need the circumflex accent on a letter like â, just type it normally or use the symbolic notation \^a (see section 2.6).

&

The ampersand is used in LATEX tables to separate the columns (see section 6.3). If you want to print AT&T you must type AT\&T.

_

The underscore in mathematics lets you type \(r_2\) for r₂. If you want to underline text (extremely rare in typesetting) see the last paragraph in section 8.2.3. If you need an underscore character as part of a program variable name like SUB_TOTAL, use the \verb command (see section 6.6).

˜

The tilde in LATEX prints as a normal space, but prevents a linebreak ever occurring at that point. It's often used between a person's initials and their surname, e.g. Prof D.E.~Knuth where a linebreak would make it harder to read.

#

If you want a hash mark (the octothorpe or American ‘pound’ [weight] or ‘number’ sign) you must type \#. For a pound (sterling) sign (£, now nearly obsolete except in the UK and some of its former dependencies), use your £ key or type \textsterling.

While we're on the subject of money, the official sans-serif Euro sign € needs the marvosym package and is done with the \EUR command (see section 5.1 for details of how to use LATEX packages). Not every font has a Euro character, though, and the default € is based on a letter C. However, a slightly unusual but interesting serif Euro sign € is in the textcomp package using the \texteuro command when using the Computer Modern typeface (see section 8.2.2 for details of switching typefaces in mid-text).

2.7.1 Specifying size units

Most people in printing and publishing in English-speaking cultures habitually use points, picas and ems; and their designers may also use cm and mm, especially when dealing with clients. Many older English-language speakers still use inches. In other cultures, [Didot] points and [Cicero] picas are also used professionally, but cm and mm are standard: inches are used only when communicating with North American cultures.

You can specify lengths in LATEX in any of these units, plus some others (see Table 2.1).

The em can cause beginners some puzzlement because it's based on the ‘point size’ of the type, which is itself misleading. The point size refers to the depth of the metal body on which foundry type was cast in the days of metal typesetting, not the printed height of the letters themselves. Thus the letter-size of 10pt type in one typeface can be radically different from 10pt type in another (look at Figure 2.1, where the widths are given for 10pt type). An em is the height of the type-body in a specific size, so 1em of 10pt type is 10pt and 1em of 24pt type is 24pt. A special name is given to the 12pt em, a ‘pica’ em, and a pica has become a fixed measure in its own right. An old name for a 1em space is a ‘quad’, and LATEX has a command \quad for leaving exactly that much horizontal space.

To highlight the differences between typefaces at the same size, Figure 2.1 shows five capital Ms in different faces, surrounded by a box exactly 1em of those sizes wide, and showing the actual width of each M when set in 10pt type. Because of the different ways in which typefaces are designed, none of them is exactly 10pt wide.

If you are working with other DTP users, watch out for those who think that Adobe points (bp) are the only ones. The difference between an Adobe big-point and the standard point is only .27pt per inch, but in 10″ of text (a full page of A4) that's 2.7pt, which is nearly 1mm, enough to be clearly visible if you're trying to align one sample with another.

2.7.2 Hyphenation

LATEX hyphenates automatically according to the language you use (see section 2.7.6). To specify different breakpoints for an individual word, you can insert soft-hyphens (discretionary hyphens, done with \-) wherever you need them, for example:

When in Mexico, we visited Popoca\-tépetl by helicopter.

To specify hyphenation points for all occurrences of a word in the document, use the \hyphenation command in your preamble (see the panel ‘The Preamble’ in section 3.4) with one or more words as patterns in its argument, separated by spaces. This will even let you break ‘helico-
pter’ correctly. In this command you use normal hyphens in the pattern, not soft-hyphens.

\hyphenation{helico-pter Popoca-tépetl im-mer-sion}

If you have frequent hyphenation problems with long, unusual, or technical words, ask an expert about changing the value of \spaceskip, which controls the flexibility of the space between words. This is not something you would normally want to do without advice, as it can change the appearance of your document quite significantly.

If you are using a lot of unbreakable text (see the next section and also section 6.6.1) it may also cause justification problems. One possible solution to this is shown in section 9.3.

2.7.3 Unbreakable text

This is the opposite of discretionary hyphenation. To force LATEX to treat a word as unbreakable, use the \mbox command:\mbox{pneumonoultramicroscopicsilicovolcanoconiosis}.
This may have undesirable results, however, if you subsequently change margins or the width of the text: pneumonoultramicroscopicsilicovolcanoconiosis...

To tie two words together with an unbreakable space (hard space), use a tilde (~) instead of the space (see the item ‘˜’). This will print as a normal space but LATEX will never break the line at that point. You should make this standard typing practice for things like people's initials followed by their surname, as in Prof. D.E. Knuth: Prof.\ D.E.~Knuth.

  Spacing after full points (periods)

Note that a full point (period) after a lowercase letter is treated in LATEX as the end of a sentence, and it automatically puts a little more space before the next word. You do not (and should not) type extra space yourself.

However, after abbreviations in mid-sentence like ‘Prof.’, it's not the end of a sentence, so we can use backslash-space to force LATEX to treat it as an ordinary word-space, because it's OK to break the line after ‘Prof.’, whereas it would look wrong to have initials separated with Prof. D.
E. Knuth broken at a line-end.

2.7.4 Dashes

For a long dash — what printers call an ‘em rule’ like this — use three hyphens typed together, like~--- this, and bind them to the preceding word with a tilde to avoid the line being broken before the dash. It's also common to see the dash printed without spaces—like that: the difference is purely æsthetic. Never use a single hyphen for this purpose.

Between digits like page ranges (35–47), it is normal to use the short dash (what printers call an en-rule) which you get by typing two hyphens together, as in 35--47. If you want a minus sign, use math mode (section 2.8). Never use a single hyphen for either of these purposes.

2.7.5 Justification

The default mode for typesetting in LATEX is justified (two parallel margins, with word-spacing adjusted automatically for the best optical fit). In justifying, LATEX will never add space between letters, only between words. The soul package can be used if you need letter-spacing, but this is best left to the expert.

There are two commands \raggedright and \raggedleft which typeset with only one margin aligned. Ragged-right has the text ranged (aligned) on the left, and ragged-left has it aligned on the right. They can be used inside a group to confine their action to a part of your text, or put in the Preamble if you want the whole document done that way.

These modes also exist as environments called raggedright and raggedleft which are more convenient when applying this formatting to a whole paragraph or more, like this one.

\begin{raggedleft} 
These modes also exist as environments called raggedright 
and raggedleft which is more convenient when applying this 
formatting to a whole paragraph or more, like this one.
\end{raggedleft}

Ragged setting turns off hyphenation. There is a package ragged2e which retains hyphenation in ragged setting, useful when you have a lot of long words.

To centre text, use the \centering command in a group, or use the center environment.

Be careful when centering headings or other display-size material, and add manual linebreaks where needed (\\) to make the breaks at sensible pauses in the meaning.

2.7.6 Languages

LATEX can typeset in the native manner for several dozen languages. This affects hyphenation, word-spacing, indentation, and the names of the parts of documents displayed in headings (but not the commands used to produce them).

Most distributions of LATEX come with US English and one or more other languages installed by default, but it is easy to add the babel package and specify any of the supported languages or variants, for example:

\usepackage[english,german,frenchb]{babel}
...
\selectlanguage{german}

Make sure that the base language of the document comes last in the list. Changing the language with babel automatically changes the names of the structural units and identifiers like ‘Abstract’, ‘Index’, etc. to their translated version. For example, using French as above, chapters will start with ‘Chapitre’. The babel package also sets the hyphenation patterns provided your version of LATEX has them precompiled (see the start of your log files for a list). For other languages you need to set the hyphenation separately (outside the scope of this book).