Obj. 5: Further, mode, species and order are caused by weight,
number and measure, as appears from the quotation from Augustine. But
not every good thing has weight, number and measure; for Ambrose says
(Hexam. i, 9): "It is of the nature of light not to have been created
in number, weight and measure." Therefore the essence of goodness does
not consist in mode, species and order.

_On the contrary,_ Augustine says (De Nat. Boni. iii): "These
three--mode, species and order--as common good things, are in
everything God has made; thus, where these three abound the things are
very good; where they are less, the things are less good; where they
do not exist at all, there can be nothing good." But this would not be
unless the essence of goodness consisted in them. Therefore the
essence of goodness consists in mode, species and order.

_I answer that,_ Everything is said to be good so far as it is perfect;
for in that way only is it desirable (as shown above, AA. 1, 3). Now
a thing is said to be perfect if it lacks nothing according to the
mode of its perfection. But since everything is what it is by its form
(and since the form presupposes certain things, and from the form
certain things necessarily follow), in order for a thing to be perfect
and good it must have a form, together with all that precedes and
follows upon that form. Now the form presupposes determination or
commensuration of its principles, whether material or efficient, and
this is signified by the mode: hence it is said that the measure marks
the mode. But the form itself is signified by the species; for
everything is placed in its species by its form. Hence the number is
said to give the species, for definitions signifying species are like
numbers, according to the Philosopher (Metaph. x); for as a unit added
to, or taken from a number, changes its species, so a difference added