The single most confusing thing for LaTeX beginners is how line breaks and paragraph breaks work. There are really just two keys: a blank line starts a new paragraph, and **\\ breaks a *line*, not a paragraph.** Grasp that distinction and you avoid the classic beginner mistake of hammering \\ to separate paragraphs. We will also cover how to control first-line indentation and the gap between paragraphs.
A blank line starts a paragraph
In LaTeX, one or more blank lines (a line that is empty or contains only spaces or tabs) separate paragraphs. Conversely, a single line break in your source is treated as just one space in the output — the sentences stay joined. LaTeX itself decides where to break lines; the newline keys you press in the manuscript do not affect the final line breaks. This is LaTeX’s core idea of separating the *look of the source* from the *look of the output*; the fine points of whitespace are also covered on the “Syntax rules” page.
Look at the source below. The first part is written across three lines, but in the output it becomes one continuous paragraph. Only where a blank line appears does a new paragraph begin. Note that stacking several blank lines has the same effect as one — you still get just one paragraph break.
これらの 3 行は
ソースでは改行していますが、
出力では 1 つの段落になります。
空行をはさんだので、ここから新しい段落です。Writing the **\par** command instead of a blank line breaks the paragraph in exactly the same way. \par is useful where a blank line is not allowed (for example inside the definition of your own command), but in ordinary body text a blank line reads more clearly and is preferred. Conversely, you cannot put a blank line inside the argument of \section{...} or in math mode — doing so raises an error.
Line breaks are not paragraph breaks
This is the crucial point. **\\ (two backslashes) and \newline force a *line* break inside a paragraph** — they do not separate paragraphs. \\ merely marks “end the line here”; it does not leave horizontal mode or end the paragraph. So using \\ to split paragraphs is wrong. The official reference says it outright: “don’t start new paragraphs with \\. Instead leave a blank line between the two paragraphs.”
Why is this a problem? Because splitting paragraphs with \\ gives you no first-line indent, no inter-paragraph spacing, and a last line that is not justified to the margin. The result is a half-formed look: the text breaks, but it does not read as a real paragraph. The rule of thumb: always end a paragraph with a blank line (or \par), and use \\ only for a forced break *within* a line.
\\ has handy extensions. Writing a length in square brackets, as in \\[2ex], adds extra vertical space after that line (a negative value is allowed too). This is common in tables (tabular) and displayed-math environments when you want to open up the leading. The form \\* forbids a page break at that line break, keeping the two lines on the same page. Note that using \\ where there is no line to end (such as at the very start of a paragraph) gives the error There's no line here to end.
So how do \newline and \linebreak differ? In paragraph mode **\newline is exactly like \\ — it breaks without stretching the line. \linebreak, by contrast, breaks at that point *and* stretches the spaces so the text justifies to the right margin**, which can leave gappy word spacing. Writing \linebreak[n] (n from 0 to 4) sets how insistent the break is: 4 forces it, 1 is a mild “if possible” request. Inside tables it also helps to remember that \newline breaks only within a cell, while \\ breaks the whole row.
Controlling indentation
By default LaTeX indents the first line of every paragraph — except the first paragraph right after a heading (such as \section), which is not indented, following traditional English typesetting. In Japanese typesetting a full-width first-line indent is normal, so Japanese classes adjust these defaults accordingly.
To toggle indentation per paragraph, use two commands. Putting **\noindent at the start of a paragraph suppresses its indent (also handy when continuing an interrupted paragraph). Conversely, \indent** forces an indent, internally emitting an empty box of width \parindent. Neither has any effect mid-paragraph, since the indentation decision has already been made there.
The amount of indentation itself is set by the length **\parindent. In the standard classes (one-column) its defaults are 15pt at 10pt text, 17pt at 11pt, 1.5em at 12pt, and 1em in two-column mode. The vertical space inserted before each paragraph is the length \parskip, whose standard-class default is 0pt plus1pt** (essentially zero, with a tiny bit of stretch). Change either with \setlength, normally in the preamble.
\setlength{\parindent}{2em} % 字下げを 2em に
\setlength{\parskip}{6pt} % 段落間に 6pt の空きBlock paragraphs & the parskip package
For business documents or web-like layouts, a “block paragraph” style — no first-line indent, paragraphs separated by vertical space — is often preferred. The naive way is to zero \parindent and give \parskip some space in the preamble. Here is the minimal form.
\setlength{\parindent}{0pt}
\setlength{\parskip}{\baselineskip}But enlarging \parskip by hand has a side effect: places that reuse the inter-paragraph gap — the table of contents, lists, figure surroundings — also stretch out. The **parskip package** handles this cleanly; you just write \usepackage{parskip}. By default it sets \parindent to 0pt and \parskip to .5\baselineskip plus 2pt, while taming the table-of-contents glitches. The stretchable plus glue also helps LaTeX find better page-break points. If you want to keep indentation, request it via an option, as in \usepackage[indent]{parskip}.
Page breaks and non-breaks
A paragraph break and a page break are different things. **\newpage ends the current page and moves to the next, but it does not split a paragraph. \clearpage** goes further, flushing all pending floats (figures and tables) before changing pages. Use neither when your goal is merely a new paragraph. Finer control of line and page breaks is covered on the “Tuning line breaks” and “Tuning page breaks” pages.
There are also tools for the opposite — preventing a break. The tilde **~ is a non-breaking space**: it keeps what is on either side of it on the same line, as in Fig.~3 or Dr.~Smith. **\, is a thin space, used for instance between a number and its unit. Neither breaks a line or a paragraph**; they are spacing adjustments whose role is clearly distinct from line and paragraph breaks.