The Functions of Boldface
Boldface type, which has a heavier weight than, meaning it is thicker than, roman type, is employed to provide emphasis but has a prescribed set of uses. This post outlines those uses.
In running text—the default wording in a piece of context, as opposed to display copy, which consists of headings, subheadings, captions, footnotes, sidebars, and other special text—boldface is appropriate only in certain circumstances. In printed and online publications, it is most often employed in educational contexts, where newly introduced terms may be bolded, or styled in boldface, to signal to a reader that such terms are key to understanding the topic under discussion.
For example, in textbooks, words introduced as new vocabulary are often formatted in boldface within the running text. At the beginning of each chapter or section, these words may be listed in a sidebar, and they may be defined in footnotes or in a glossary, or list of terms and definitions, at the end of the section or the book. In most other cases, using boldface in running text is an aesthetic choice, often for humorous effect or, for example, to represent shouting in a children’s storybook.
Display copy is often boldface to distinguish it from the running text, although such content is generally styled in a different font and in larger point sizes for that reason. Run-in subheads or sideheads—those that begin a paragraph or a section of type rather than appear on a line above it, and that are generally formatted the same point size as the rest of the paragraph or section—are often boldfaced to distinguish them from the narrative that follows. (Such subheads are, alternatively, often italicized.)
Punctuation following a run-in subhead, whether a period, a colon, or a dash, should also be boldface. And when, for example, glossary terms are boldfaced, if punctuation follows each term before the definitions, the punctuation should be boldfaced. This is also true for figure headings (where, for example, “Figure 1.” or “Figure 1:” precedes the title of the figure) and captions, where directional terms such as above or left may be boldfaced or where a run-in heading may precede a caption’s explanatory text.
However, in running text, punctuation that follows a boldfaced term, because it is associated with the surrounding text, not with the emphasized element, is not boldfaced. (This is true even if the boldfaced term is enclosed in parentheses or bracketed by a pair of commas or dashes.)
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