The point of morals is happiness and since law enforces morality,
it stands to reason that the point of law is also happiness, which
for Aquinas is indeed the case.
Aquinas defines law as "an act of reason planning action
to serve the ultimate goal of happiness, specifically the happiness
of individuals living in community." (1a2ae, 90, 2)
Being a philosopher, Aquinas likes to bring things down to their
most basic level and he does this in the foundation of his thoughts
on law. He says when we figure things out, the first thing we
grasp is that things either exist or they don't exist. We recognize
we exist, even though we don't necessarily know why (and give
the name God to the mysterious cause of our existence). Then he
says it's natural for existing, living things to flourish and
grow; that's just what life does and it's something we recognize
as obvious (i.e., truths that are self-evident). The measure of
this flourishing (as we have said) is what he calls goodness;
the closer we are to fulfilling our natural potential, the more
"good" we are, and this flourishing and fulfillment
is what we naturally seek and is what will naturally make us the
Just as all thought is based on a grasp of being (however mysterious
it might be), all action is based on a grasp of good, because
action always seeks good as its goal. Aquinas therefore defines
law as an act of reason planning action based on the fact that
lifeforms seek their own good (i.e., to grow into their own potential).
So the primary law, upon which all other laws must be based, is
that good be done (i.e., fourishing occur) and evil avoided.
This is what Aquinas calls natural law, and this is the third
key idea of Part Two of the Summa.
"Since good is grasped as always desireable, the first
premise in reason's planning of action is that good is to be
done and evil avoided. And on this are based all the other injunctions
of the law in us by nature, which command us to do whatever
reason, when planning action, naturally grasps to be good for
man, whatever man naturally seeks as a goal."
We figure out what makes humans thrive and derive morality and
law from that.
Aquinas points out three obvious derivatives of natural law:
1) Stay alive; conserve human life and oppose death.
2) Do whatever accords with our physical nature, which is what
we have in common with other animals (e.g., having sex, having
3) Do whatever accords with our rational nature, like "to
know the truth about God, for example, and to live a social
life." Therefore, this means "avoiding ignorance and
not offending those we live with."
Natural law and its obvious derivatives are all well and good.
However, it can get tricky when we try and apply them to the particulars,
which is what we do when we construct human law.
"Planning for the general good belongs to the people as
a whole or to someone representing them, since those pursuing
the goal must do the planning for it."
(1a2ae, 90, 1)
"Tyrannical law, being unreasonable, is not truly law but
a breakdown of law."
(1a2ae, 90, 2)
"We hold these truths to be self-evident, that all men
are created equal, that they are endowed by their Creator with
certain unalienable Rights, that among these are Life, Liberty,
and the pursuit of Happiness."
Declaration of Independence