Mirth the expression of joy, gayety, merriment, is thus distinguished from its synonym, cheerfulness: Mirth is considered as an act, cheerfulness a habit of the mind. Mirth is short and transient; cheerfulness fixed and permanent.
Those are often raised into the greatest transports of mirth who are subject to the greatest depressions of melancholy: on the contrary, cheerfulness, though it does not give such an exquisite gladness, prevents us from falling into any depths of sorrow. Mirth is like a flash of lightning, that breaks through a gloom of clouds, and glitters for a moment; cheerfulness keeps up a kind of daylight in the mind, and fills it with a steady and perpetual serenity.
Mirth is sinful,
1. When men rejoice in that which is evil. 2. When unreasonable. 3. When tending to commit sin. 4. When a hinderance to duty. 5. When it is blasphemous and profane.