Guide to LaTeX (4th Edition) (Tools and Techniques

32 Chapter 2. Text, Symbols, and Commands
where num is an optional argument, a number between 0 and 4 that
specifies how important a line break is. The command recommends a line
break, and the higher the number the stronger the recommendation. A
value of 0 allows a break where it otherwise would not occur (like in the
middle of a word), whereas 4 compels a line break, as does \linebreak
without num. The difference between this command and \\ or \newline
is that the current line will be fully justified, that is, interword spacing will
be added so that the text fills the line completely. With \\ and \newline,
however, the line is filled with empty space after the last word and the
interword spacing remains normal.
The opposite command
\nolinebreak[num]
discourages a line break at the given position, with num specifying the
degree of discouragement. Again, \nolinebreak without a num argument
has the same effect as \nolinebreak[4], that is, a line break is
absolutely impossible here.
Another way of forcing text to stay together on one line is with the command
\mbox{text}. This is convenient for expressions such as ‘Voyager-1’
to stop a line break at the hyphen.
2.7.3 Vertical spacing
It is possible to add extra vertical spacing of amount space between
particular paragraphs using the commands
\vspace{space}
\vspace*{space}
The *-form will add the extra space even when a new page occurs, or
when the command appears at the top of a new page. The standard form
ignores the extra vertical spacing in these situations.
If these commands are given within a paragraph, the extra space is
inserted after the current line, which is right and left justified as usual.
The space parameter may even be negative, in order to move the
following text higher up the page than where it would normally be printed.
The command \vfill is an abbreviation for \vspace{\fill} (see
Section 2.4.2). This is the equivalent of \hfill for vertical spacing,
inserting enough blank vertical space to make the top and bottom of the
text match up exactly with the upper and lower margins. The comments
on multiple occurrences of \hfill also apply to \vfill. If this command
is given at the beginning of a page, it is ignored, just like the standard
form of \vspace{\fill}. If a rubber space is to be put at the top of a
page, the *-form \vspace*{\fill} must be used.
Further commands for increasing the spacing between paragraphs are