The number of examples you use in a sentence has meaning.

Use one example for power.
That girl is smart. The writer declares her intelligence.

Use two for comparison, contrast.
That girl is smart and sweet. The writer asks us to weigh these two attributes.

Use three for completeness, wholeness.
That girl is smart, sweet and determined. The writer rounds out her character.

Use four or more to list, inventory, compile and expand.
That girl is smart, sweet, determined and anorexic. With four (or more) details, the writer achieves “escape velocity,” going beyond the sense of completion to create flowing language and fresh literary effects.

Taken from The Writer's Workbench: 50 Tools You Can Use, a self-directed course by Roy Peter Clark at Poynter NewsU.

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