There is an inconvenience which attends all abstruse reasoning, that it may silence, without convincing an antagonist, and requires the same intense study to make us sensible of its force, that was at first requisite for its invention. When we leave our closet, and engage in the common affairs of life, its conclusions seem to vanish, like the phantoms of the night on the appearance of the morning; and ’tis difficult for us to retain even that conviction, which we had attain’d with difficulty.

Morality is a subject that interests us above all others: We fancy the peace of society to be at stake in every decision concerning it; and ’tis evident, that this concern must make our speculations appear more real and solid, than where the subject is, in a great measure, indifferent to us. What affects us, we conclude can never be a chimera; and as our passion is engag’d on the one side or the other, we naturally think that the question lies within human comprehension; which, in other cases of this nature, we are apt to entertain some doubt of. Without this advantage I never should have ventur’d upon a third volume of such abstruse philosophy, in an age, wherein the greatest part of men seem agreed to convert reading into an amusement, and to reject every thing that requires any considerable degree of attention to be comprehended.