Why does \textbf not make Greek symbols bold in LaTeX math mode?

The \textbf command works only in text mode and does not affect symbols inside math mode. Greek letters such as \alpha or \beta are mathematical symbols, so they require math-specific commands like \boldsymbol or \bm to appear in bold.

What is the best command to make Greek letters bold in LaTeX?

The most reliable command is \bm from the bm package. It correctly bolds Greek symbols and other mathematical characters.

Why does \mathbf not work for bold Greek symbols?

\mathbf works mainly for Latin letters and numbers in math mode. Greek symbols belong to a different math font family, so \mathbf usually does not affect them. Instead, commands like \boldsymbol or \bm should be used.

Do I need to load a package to use \boldsymbol or \bm in LaTeX?

Yes. The \boldsymbol command is available through the amsmath package, while \bm comes from the bm package.

Fix Bold Greek Symbol Problem in LaTeX Math Mode

A common problem in LaTeX appears when someone tries to bold Greek letters such as \alpha, \beta, or \lambda. Even after using \textbf or \mathbf, the symbol remains unchanged.

Table of Contents

Make Greek symbols bold with amsmath package
Heavier math style using bm command
Best Practice

This happens because Greek symbols behave differently in math mode, so special commands are needed.

Make Greek symbols bold with amsmath package

When writing mathematical documents, many people already load the amsmath package.

This package provides two useful commands: \boldsymbol and \pmb. These commands allow you to apply bold styling to mathematical symbols including Greek letters.

They are helpful when writing vector quantities, parameters, or emphasized symbols in equations.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
 \begin{center} Default size: \end{center} 
  \[ \alpha \quad \beta \quad \gamma \quad \lambda \quad \Sigma \quad \psi \quad \varepsilon \] 
 \begin{center} Using \verb|\boldsymbol{}| command: \end{center} 
  \[ \boldsymbol{\alpha \quad \beta \quad \gamma \quad \lambda \quad \Sigma \quad \psi \quad \varepsilon} \]
 \begin{center} Using \verb|\pmb{}| command: \end{center}
  \[ \pmb{\alpha \quad \beta \quad \gamma \quad \lambda \quad \Sigma \quad \psi \quad \varepsilon} \]
\end{document}

Heavier math style using bm command

Another reliable solution is the bm package. It provides the \bm command, which is designed specifically for bold math symbols.

This method is widely used because it produces consistent results for complex mathematical expressions and bold Greek characters.

\documentclass{article}
\usepackage{bm}
\begin{document}
 \begin{center} \verb|Default size:| \end{center}
  \[ \alpha \quad \beta \quad \gamma \quad \lambda \quad \Sigma \quad \psi \quad \varepsilon \]
 \begin{center} Using \verb|\bm| command:\end{center}
  \[ \bm{\alpha \quad \beta \quad \gamma \quad \lambda \quad \Sigma \quad \psi \quad \varepsilon} \]
\end{document}