UK TeX FAQ -- question label boldgreek

### Setting bold Greek letters in LaTeX maths

The issue here is complicated by the fact that `\``mathbf` (the command for setting bold text in TeX maths) affects a select few mathematical ‘symbols’ (the uppercase Greek letters).

In the default configuration, lower-case Greek letters behave differently from upper-case Greek letters (the lower-case greek letters are in the maths fonts, while the upper-case letters are in the original (OT1-encoded) text fonts).

The Plain TeX solution does work, in a limited way; you set a maths style, before you start an equation; thus

>     {\boldmath$\theta$}

does the job, but `\``boldmath` may not be used in maths mode. As a result, this solution requires that you embed single bold characters in a text box:

>     $... \mbox{\boldmath$\theta$} ...$

which then causes problems in superscripts, etc. With amsmath loaded,

>     $... \text{\boldmath$\theta$} ...$

does the trick (and is less bad in regard to superscripts, etc), but is an unsatisfactory solution, too.

These problems may be addressed by using a bold mathematics package.

- The bm package, which is part of the LaTeX tools distribution, defines a command `\``bm` which may be used anywhere in maths mode.
- The amsbsy package (which is part of AMSLaTeX) defines a command `\``boldsymbol`, which (though slightly less comprehensive than `\``bm`) covers almost all common cases.

All these solutions apply to all mathematical symbols, not merely Greek letters.

`bm.sty`
  Distributed as part of macros/latex/required/tools (or browse the directory); catalogue entry
`amsbsy.sty`
  Distributed as part of AMSLaTeX macros/latex/required/amslatex (or browse the directory); catalogue entry
`amsmath.sty`
  Distributed as part of AMSLaTeX macros/latex/required/amslatex (or browse the directory); catalogue entry

This answer last edited: 2013-06-12

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