[Tex/LaTex] Purpose of “control space”

Question

I could not find enough information on Google about control space (\). What is the purpose of it? Where should it be used?

Answer 1

The following is taken directly from Knuth's TeXbook (Chapter 3: Controlling TeX, p 8):

When a space comes after a control word (an all-letter control sequence), it is ignored by TeX; i.e., it is not considered to be a "real" space belonging to the manuscript that is being typeset. But when a space comes after a control symbol, it's truly a space.

Now the question arises, what do you do if you actually want a space to appear after a control word? We will see later that TeX treats two or more consecutive spaces as a single space, so the answer is not going to be "type two spaces." The correct answer is to type "control space," namely

\␣

(the escape character followed by a blank space); TeX will treat this as a space that is not to be ignored. Notice that control-space is a control sequence of the second kind, namely a control symbol, since there is a single nonletter (␣) following the escape character. Two consecutive spaces are considered to be equivalent to a single space, so further spaces immediately following \␣ will be ignored. But if you want to enter, say, three consecutive spaces into a manuscript you can type \␣\␣\␣. Incidentally, typists are often taught to put two spaces at the ends of sentences; but we will see later that TeX has its own way to produce extra space in such cases. Thus you needn't be consistent in the number of spaces you type.

For example, compare

\TeX\ ignores spaces after control words.

to

\TeX ignores spaces after control words.