Truth is of two kinds, consisting either in the discovery of the proportions of ideas, considered as such, or in the conformity of our ideas of objects to their real existence.  It is certain, that the former species of truth, is not desired merely as truth, and that it is not the justness of our conclusions, which alone gives the pleasure.  For these conclusions are equally just, when we discover the equality of two bodies by a pair of compasses, as when we learn it by a mathematical demonstration; and though in the one case the proofs be demonstrative, and in the other only sensible, yet generally speaking, the mind acquiesces with equal assurance in the one as in the other.  And in an arithmetical operation, where both the truth and the assurance are of the same nature, as in the most profound algebraical problem, the pleasure is very inconsiderable, if rather it does not degenerate into pain:  Which is an evident proof, that the satisfaction, which we sometimes receive from the discovery of truth, proceeds not from it, merely as such, but only as endowed with certain qualities.

The first and most considerable circumstance requisite to render truth agreeable, is the genius and capacity, which is employed in its invention and discovery.  What is easy and obvious is never valued; and even what is in itself difficult, if we come to the knowledge of it without difficulty, and without any stretch of thought or judgment, is but little regarded.  We love to trace the demonstrations of mathematicians; but should receive small entertainment from a person, who should barely inform us of the proportions of lines and angles, though we reposed the utmost confidence both in his judgment and veracity.  In this case it is sufficient to have ears to learn the truth.  We never are obliged to fix our attention or exert our genius; which of all other exercises of the mind is the most pleasant and agreeable.

But though the exercise of genius be the principal source of that satisfaction we receive from the sciences, yet I doubt, if it be alone sufficient to give us any considerable enjoyment.  The truth we discover must also be of some importance.  It is easy to multiply algebraical problems to infinity, nor is there any end in the discovery of the proportions of conic sections; though few mathematicians take any pleasure in these researches, but turn their thoughts to what is more useful and important.  Now the question is, after what manner this utility and importance operate upon us?  The difficulty on this head arises from hence, that many philosophers have consumed their time, have destroyed their health, and neglected their fortune, in the search of such truths, as they esteemed important and useful to the world, though it appeared from their whole conduct and behaviour, that they were not endowed with any share of public spirit, nor had any concern for the interests of mankind.  Were they convinced, that their discoveries were of no consequence, they would entirely lose all relish for their studies, and that though the consequences be entirely indifferent to them; which seems to be a contradiction.