But notwithstanding this frequent confusion of interests, it is easy to attain what natural philosophers, after Lord Bacon, have affected to call the experimentum crucis, or that experiment which points out the right way in any doubt or ambiguity.  We have found instances, in which private interest was separate from public; in which it was even contrary:  And yet we observed the moral sentiment to continue, notwithstanding this disjunction of interests.  And wherever these distinct interests sensibly concurred, we always found a sensible increase of the sentiment, and a more warm affection to virtue, and detestation of vice, or what we properly call, gratitude and revenge.  Compelled by these instances, we must renounce the theory, which accounts for every moral sentiment by the principle of self-love.  We must adopt a more public affection, and allow, that the interests of society are not, even on their own account, entirely indifferent to us.  Usefulness is only a tendency to a certain end; and it is a contradiction in terms, that anything pleases as means to an end, where the end itself no wise affects us.  If usefulness, therefore, be a source of moral sentiment, and if this usefulness be not always considered with a reference to self; it follows, that everything, which contributes to the happiness of society, recommends itself directly to our approbation and good-will.  Here is a principle, which accounts, in great part, for the origin of morality:  And what need we seek for abstruse and remote systems, when there occurs one so obvious and natural?

[Footnote:  It is needless to push our researches so far as to ask, why we have humanity or a fellow-feeling with others.  It is sufficient, that this is experienced to be a principle in human nature.  We must stop somewhere in our examination of causes; and there are, in every science, some general principles, beyond which we cannot hope to find any principle more general.  No man is absolutely indifferent to the happiness and misery of others.  The first has a natural tendency to give pleasure; the second, pain.  This every one may find in himself.  It is not probable, that these principles can be resolved into principles more simple and universal, whatever attempts may have been made to that purpose.  But if it were possible, it belongs not to the present subject; and we may here safely consider these principles as original; happy, if we can render all the consequences sufficiently plain and perspicuous!]

Have we any difficulty to comprehend the force of humanity and benevolence?  Or to conceive, that the very aspect of happiness, joy, prosperity, gives pleasure; that of pain, suffering, sorrow, communicates uneasiness?  The human countenance, says Horace [’Uti ridentibus arrident, ita flentibus adflent Humani vultus,’—­ Hor.], borrows smiles or tears from the human countenance.  Reduce a person to solitude, and he loses all enjoyment, except either of the sensual or speculative kind; and that