Does the natural law contain many
precepts or just one precept?
It seems that the natural law contains
just one precept and not many precepts:
Objection 1: As was
explained above (q. 92, a. 2), law is contained under
the genus precept. Therefore, if the natural
law contained many precepts, it would follow that there
are likewise many natural laws.
The natural law follows upon the nature of man. But a
human nature is one taken as a whole, even though it has
multiple parts. Therefore, either (a) there is just one
precept of the law of nature because of the oneness of the
whole or (b) there are many precepts because of the
multiplicity of the parts of a human nature—in which case
even what stems from the inclination of the concupiscible
[part of the soul] will belong to the natural law.
As was explained above (q. 90, a. 1), law is something
that belongs to reason. But there is just a single
faculty of reason in a man. Therefore, the natural law
contains just one precept.
But contrary to this:
The precepts of the natural law play the same role in a
man with respect to matters of action that first
principles play with respect to matters of demonstration.
But there are many indemonstrable first principles.
Therefore, there are likewise many precepts of the natural
As was explained above (a. 1), the precepts of the law
of nature bear the same relation to practical reason
that the first principles of demonstration bear to speculative
reason. For they are both principles that are
known per se (per se nota).
Now there are two senses in which something is said
to be known per se: (a) in its own right
(secundum se) and (b) as regards us (quoad
Every proposition (propositio) said to be known
per se in its own right is such that its predicate
is part of the notion of its subject (de ratione
subiecti); and yet it happens that such a proposition
will not be known per se to someone who does
not know the definition of the subject. For instance,
the proposition ‘A man is rational’ is known per
se given its own nature, since anyone who expresses
man expresses rational; and yet this proposition
is not known per se to someone who does not know
the real definition (quid sit) of man.
This is why, as Boethius points out in De Hebdomadibus,
certain fundamental truths (dignitates) and propositions
(propositiones) are known per se in general
to everyone—and these are the ones whose terms are known
to everyone, e.g., ‘Every whole is greater than its
part’ and ‘Things equal to one and the same thing are
equal to one another’—whereas other propositions are
known per se only to the wise, who understand
what the terms of the proposition signify. For
instance, to someone who understands that an angel is
not a body it is known per se that an angel does
not exist circumscriptively in a place; however, this
is not obvious to unsophisticated people, who do not
grasp the point in question.
Now there is a certain order among those things that
fall within everyone’s apprehension. The first
thing to fall within apprehension is being, a
grasp of which is included in everything that anyone
apprehends. So the first indemonstrable principle,
founded upon the notions being and non‑being,
is ‘One is not to affirm and deny [the same thing] at
the same time’. And, as Metaphysics 4
says, all the other principles are founded upon this
Now just as being is the first thing to fall
within apprehension absolutely speaking, so good
is the first thing to fall within the apprehension of
practical reason, which is ordered toward action.
For every agent acts for the sake of an end, which has
the character of a good. And so the first principle
in practical reasoning is what is founded on the notion
good, which is the notion (supra rationem
boni quae est): “The good is what all things
desire.” Therefore, the first precept of law is
that good ought to be done and pursued and that evil
ought to be avoided. And all the other precepts
of the law of nature are founded upon this principle—so
that, namely, all the things to be done or avoided that
practical reason naturally apprehends as human goods
are such that they belong to the precepts of the law
of nature. For since what is good has the character
of an end and what is bad has the character of the contrary
of an end, it follows that all the things man has a
natural inclination toward are such that (a) reason
naturally apprehends them as goods and thus as things
that ought to be pursued by action and (b) reason naturally
apprehends their contraries as evils and thus things
that ought to be avoided.
Therefore, there is an ordering of the precepts of the
natural law that corresponds to the ordering of the
First, man has an inclination toward the good with respect
to the nature he shares in common with all substances,
viz., insofar as every substance strives for the conservation
of its own esse in accord with its own nature.
And what belongs to the natural law in light of this
inclination is everything through which man’s life is
conserved or through which what is contrary to the preservation
of his life is thwarted.
Second, man has an inclination toward certain more specific
[goods] with respect to the nature that he shares in
common with the other animals. Accordingly, those
things are said to belong to the natural law which nature
teaches all the animals, i.e., the union of male and
female, the education of offspring, etc.
man has an inclination toward the good with respect
to the rational nature that is proper to him, e.g.,
man has a natural inclination toward knowing the truth
about God and toward living in society. Accordingly,
those things that are related to this sort of inclination
belong to the natural law, e.g., that a man avoid ignorance,
that he not offend the others with whom he has to live
in community, and other such things related to this
Reply to objection 1:
Insofar as all these precepts of the law of nature are
traced back to a single first principle, they have the
character of a single natural law.
Reply to objection 2:
All the inclinations of any of the parts of human nature,
e.g., the concupiscible part and the irascible part, are
relevant to the natural law insofar as they are regulated
by reason, and, as has been explained, they are traced
back to a single first precept. Accordingly, even though
the precepts of the law of nature are many in themselves,
they nonetheless share a single root.
Reply to objection 3:
Even if reason is in itself one, it nonetheless orders all
the things relating to men. Accordingly, the law of
reason contains everything that can be regulated by