Emphasis — Bold, Italic, Strikethrough

~10 min · markdown, emphasis, inline

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Three intensities of emphasis

Markdown gives you italic (*text* or _text_), bold (**text** or __text__), and bold italic (***text***). GFM adds strikethrough (~~text~~).

Asterisks vs underscores

Functionally identical for emphasis. Asterisks are usually preferred because underscores inside words (like foo_bar_baz) can confuse parsers — most CommonMark parsers treat intra-word underscores as literal, but the rule is subtle and easy to misread.

CommonMark flanking rules

Emphasis delimiters must be 'flanking' — adjacent to non-whitespace on the correct side. ** not bold ** with spaces inside the asterisks won't work. The flanking rule prevents accidental emphasis when you mean literal asterisks.

Principle: Use emphasis as the syntactic equivalent of voice — italic for first introduction of a term, bold for keywords your reader must not miss, ***both*** almost never. If everything is emphasized, nothing is.

Code

All four kinds·markdown

*italic* or _italic_
**bold** or __bold__
***bold italic*** or ___bold italic___
~~strikethrough~~ (GFM)

Nesting·markdown

*This is **bold** inside italic*
**This is *italic* inside bold**

Intra-word: foo_bar_baz stays literal.
Use foo*bar*baz only if you want italic 'bar'.

External links

Exercise

Write three sentences using each emphasis level (italic, bold, bold-italic) in a way that earns the emphasis — the meaning would change if you removed it. If you can't justify it, you don't need it.

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