respect of all
the rest: wherefore to this principle chiefly and mainly law must
needs be referred. Now the first principle in practical matters,
which are the object of the practical reason, is the last end: and
the last end of human life is bliss or happiness, as stated above (Q.
2, A. 7; Q. 3, A. 1). Consequently the law must needs regard
principally the relationship to happiness. Moreover, since every part
is ordained to the whole, as imperfect to perfect; and since one man
is a part of the perfect community, the law must needs regard
properly the relationship to universal happiness. Wherefore the
Philosopher, in the above definition of legal matters mentions both
happiness and the body politic: for he says (Ethic. v, 1) that we
call those legal matters "just, which are adapted to produce and
preserve happiness and its parts for the body politic": since the
state is a perfect community, as he says in _Polit._ i, 1.

Now in every genus, that which belongs to it chiefly is the principle
of the others, and the others belong to that genus in subordination
to that thing: thus fire, which is chief among hot things, is the
cause of heat in mixed bodies, and these are said to be hot in so far
as they have a share of fire. Consequently, since the law is chiefly
ordained to the common good, any other precept in regard to some
individual work, must needs be devoid of the nature of a law, save in
so far as it regards the common good. Therefore every law is ordained
to the common good.

Reply Obj. 1: A command denotes an application of a law to matters
regulated by the law. Now the order to the common good, at which the
law aims, is applicable to particular ends. And in this way commands
are given even concerning particular matters.

Reply Obj. 2: Actions are indeed concerned with particular matters:
but those particular matters are referable to the common good, not as
to a common genus or species, but as to a common final cause,
according as the common good is said to be the common end.

Reply Obj. 3: Just as nothing stands firm with regard to the
speculative reason except that which is traced back to the first
indemonstrable principles, so nothing stands firm with regard to the
practical reason, unless it be directed to the last end which is the
common good: and whatever stands to reason in this sense, has the
nature of a law.
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THIRD ARTICLE [I-II, Q. 90, Art. 3]

Whether the Reason of Any Ma