Chapter VI. considers Fitness and Moral Obligation, and other prevailing forms of expression regarding morality.  Fitness and Unfitness denote Congruity or Incongruity, and are necessarily a perception of the Understanding.

The term Obligation is more perplexing.  Still, it is but another name for Rightness.  What is Right is, by that very fact, obligatory.  Obligation, therefore, cannot be the creature of law, for law may command what is morally wrong.  The will of God enforced by rewards and punishments cannot make right; it would only determine what is prudent.  Rewards and punishments do not make obligation, but suppose it.  Rectitude is a LAW, the authoritative guide of a rational being.  It is Supreme, universal, unalterable, and indispensable.  Self-valid and self-originated, it stands on immovable foundations.  Being the one authority in nature, it is, in short, the Divine authority.  Even the obligations of religion are but branches of universal rectitude.  The Sovereign Authority is not the mere result of his Almighty Power, but of this conjoined with his necessary perfections and infinite excellence.

He does not admit that obligation implies an obliger.

He takes notice of the objection that certain actions may be right, and yet we are not bound to perform them; such are acts of generosity and kindness.  But his answer throws no farther light on his main doctrine.

In noticing the theories of other writers in the same vein, as Wollaston, he takes occasion to remark that, together with the perception of conformity or fitness, there is a simple immediate perception urging us to act according to that fitness, for which no farther reason can be assigned.  When we compare innocence and eternal misery, we are struck with the idea of unsuitableness, and are inspired in consequence with intense repugnance.

Chapter VII. discusses the Heads or Divisions of Virtue; under which he enquires first what are virtuous actions; secondly, what is the true principle or motive of a virtuous agent; and thirdly, the estimate of the degrees of virtue.

He first quotes Butler to show that all virtue is not summed up in Benevolence; repeating that there is an intrinsic rectitude in keeping faith; and giving the usual arguments against Utility, grounded on the supposed crimes that might be committed on this plea.  He is equally opposed to those that would deny disinterested benevolence, or would resolve beneficence into veracity.  He urges against Hutcheson, that, these being independent and distinct virtues, a distinct sense would be necessary to each; in other words, we should, for the whole of virtue, need a plurality of moral senses.