Why are (most) spaces eliminated in \mathrm formatting? [duplicate]

Question

Why does this:

$\mathrm{The quick, brown fox jumped over the lazy dog.}$

result in this:

$\mathrm{The quick, brown fox jumped over the lazy dog.}$

Note that all spaces in my original text, save one, are missing. I have found that spaces are quite useful for separating the words in text.

Answer 1

If you want to write text in math-mode then use \text{...} or variants thereof for example:

$\text{This is some text with default font.}$

$\textrm{This is some text with specified font, which happens to coincide with the default.}$

$\textsf{This is some text in another font.}$

$\textbf{This is some text in bold.}$

$\text{This is some text with default font.}$

$\textrm{This is some text with specified font, which happens to coincide with the default.}$

$\textsf{This is some text in another font.}$

$\textbf{This is some text in bold.}$

The command \mathrm{...} is not for "text" but for letters in a particular font (namely roman) in math mode. Thus, as usual in math mode, space is ignored; if you want some you can specify it explicitly.

$\mathrm{Text \ with \ space.\; Good.}$ 

$\mathrm{Text \ with \ space.\; Good.}$

Needless to say, this is not the way to include some phrase in a mathematical part.

There are similar commands for other fonts such as:

$\mathsf{Sans}$   

$\mathbf{Bold}$   

$\mathit{Italic}$   

$\mathsf{Sans}$

$\mathbf{Bold}$

$\mathit{Italic}$