differences of things make it fit and reasonable for
creatures so to act; they cause it to be their duty, or lay an
obligation on them so to do; even separate from the consideration of
these Rules being the positive Will or Command of God, and also
antecedent to any respect or regard, expectation or apprehension of any
particular private and personal Advantage or Disadvantage, Reward or
Punishment, either present or future, annexed either by natural
consequence, or by positive appointment, to the practising or
neglecting of these rules. In the explication of this, nearly his whole
system is contained.

His first concern is to impress the fact that there are necessary and
eternal differences of ail things, and implied or consequent relations
(proportions or disproportions) existing amongst them; and to bring
under this general head the special case of differences of Persons
(e.g., God and Man, Man and Fellow-man), for the sake of the
implication that to different persons there belong peculiar _Fitnesses_
and _Unfitnesses_ of circumstances; or, which is the same thing, that
there arises necessarily amongst them a suitableness or unsuitableness
of certain manners of Behaviour. The counter-proposition that he
contends against is, that the relations among persons depend upon
_positive constitution_ of some kind, instead of being founded
unchangeably in _the nature and reason of things_.

Next he shows how, in the rational or intellectual recognition of
naturally existent relations amongst things (he always means persons
chiefly), there is contained an obligation. When God, in his
Omniscience and absolute freedom from error, is found determining his
Will always according to this eternal reason of things, it is very
unreasonable and blameworthy in the intelligent creatures whom he has
made so far like himself, not to govern their actions by the same
eternal rule of Reason, but to suffer themselves to depart from it
through negligent _misunderstanding_ or wilful _passion_. Herein lies
obligation: a man _ought_ to act according to the Law of Reason,
because he can as little refrain from _assenting_ to the reasonableness
and fitness of guiding his actions by it, as refuse his assent to a
geometrical demonstration when he understands the terms. The original
obligation of all is the eternal Reason of Things; the sanction of
Rewards and Punishments (though 'truly the most effectual means of
keeping creatures in their duty') is on