\subsection (LaTeX2e unofficial reference manual (November 2018))

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### 6.4 `\subsection`

Synopsis, one of:

    \subsection{title}
    \subsection*{title}
    \subsection[toc-title]{title}

Start a subsection. The standard LaTeX classes `article`, `book`, and `report` all have this command.

This produces a subsection.

    We will show that there are more functions than Turing machines and that
    therefore some functions have no associated machine.

    \subsection{Cardinality} We will begin with two paradoxes that
    dramatize the challenge to our intuition posed by comparing the sizes of
    infinite sets.

For the standard LaTeX classes `book` and `report` the default output is like ‘`1.2.3 title`’ (for chapter 1, section 2, subsection 3), alone on its line and flush left, in boldface and a larger type (the type size is `\large`). The same holds in `article` except that there are no chapters in that class so it looks like ‘`2.3 title`’.

The `*` form shows title. But it does not show the section number, does not increment the `section` counter, and produces no table of contents entry.

The optional argument toc-title will appear as the section title in the table of contents (see Table of contents etc.). If it is not present then title will be there. This shows the full name in the title of the section,

    \subsection[$\alpha,\beta,\gamma$ paper]{\textit{The Origin of
      Chemical Elements} by R.A.~Alpher, H.~Bethe, and G.~Gamow}

but only ‘`α,β,γ paper`’ on the contents page.

For determining which sectional units are numbered and which appear in the table of contents, the level number of a subsection is 2 (see Sectioning/secnumdepth and see Sectioning/tocdepth).

The paragraph that follows the subsection title is not indented, as is a standard typographical practice. One way to get an indent is to use the package `indentfirst`.

There are a number of ways to change the behavior of the `\subsection` command. One is the `\@startsection` command (see \@startsection). There are also many packages on CTAN that address this, including `titlesec`. See the documentation but the example below gives a sense of what they can do.

    \usepackage{titlesec}   % in preamble
    \titleformat{\subsection}[runin]
      {\normalfont\normalsize\bfseries}  % format of the title
      {\thesubsection}                   % label
      {0.6em}                            % space between label and title
      {}                                 % before-code hook

That puts the subsection number and title in the first line of text.

Unofficial LaTeX2e reference manual