The source's 'laughing' example does not require every person to be laughing at every moment. It refers to a capacity for laughter. The 'writer' example likewise concerns a capacity rather than writing at this instant.
Actually laughing now is not permanent in each person. In the classical example, capable of laughter is treated as a property of the human species.
Distinguishing potential capacity from present action prevents mistaking silence or sleep for counterexamples.
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The Five Predicables: Differentia, Property, Common Accident, Essential and Accidental Attributes
The source's 'laughing' example does not require every person to be laughing at every moment. It refers to a capacity for laughter. The 'writer' example likewise concerns a capacity rather than writing at this instant.
Actually laughing now is not permanent in each person. In the classical example, capable of laughter is treated as a property of the human species.
Distinguishing potential capacity from present action prevents mistaking silence or sleep for counterexamples.