Modes

LaTeX2e help 1.6

## 2.14: Modes

When LaTeX is processing your input text, it is always in one of three modes:

- Paragraph mode
- Math mode
- Left-to-right mode, called LR mode for short

LaTeX changes mode only when it goes up or down a staircase to a different level, though not all level changes produce mode changes. Mode changes occur only when entering or leaving an environment, or when LaTeX is processing the argument of certain text-producing commands.

``Paragraph mode'' is the most common; it's the one LaTeX is in when processing ordinary text. In that mode, LaTeX breaks your text into lines and breaks the lines into pages. LaTeX is in ``math mode'' when it's generating a mathematical formula. In ``LR mode'', as in paragraph mode, LaTeX considers the output that it produces to be a string of words with spaces between them. However, unlike paragraph mode, LaTeX keeps going from left to right; it never starts a new line in LR mode. Even if you put a hundred words into an `\mbox`, LaTeX would keep typesetting them from left to right inside a single box, and then complain because the resulting box was too wide to fit on the line.

LaTeX is in LR mode when it starts making a box with an `\mbox` command. You can get it to enter a different mode inside the box - for example, you can make it enter math mode to put a formula in the box. There are also several text-producing commands and environments for making a box that put LaTeX in paragraph mode. The box make by one of these commands or environments will be called a `parbox`. When LaTeX is in paragraph mode while making a box, it is said to be in ``inner paragraph mode''. Its normal paragraph mode, which it starts out in, is called ``outer paragraph mode''.