notions, but not right moral notions. It is true that questions of
right and wrong occur in one state of society, that had no relevance
in an earlier state, the conditions of the case not having arisen. But
so it is in architecture; there are no arches in the Parthenon. The
principle of the arch, however, held in the age of Pericles, though
not applied.

6. The progress of Moral Science is the more and more perfect
development of the Natural Law in the heart of man, a psychological,
not an ontological development. And Moral Science does progress. No
man can be a diligent student of morality for years, without coming to
the understanding of many things, for which one would look in vain in
Aristotle's _Ethics_ and _Politics_, or in Cicero, _De Officiis_, or
even in the _Summa_ of St. Thomas, or perhaps in any book ever
written. New moral questions come for discussion as civilization
advances. The commercial system of modern times would furnish a theme
for another De Lugo. And still on this path of ethical discovery, to
quote the text that Bacon loved, "Many shall pass over, and knowledge
shall be multiplied." (Daniel xii. 4.)

_Readings_.--St. Thos., Supplement, q. 65, art. 1, in corp.; _ib_., q.
65, art. 2, in corp., and ad 1; Hughes, _Supernatural Morals_, pp. 67,
68, reviewed in _The Month_ for August, 1891, pp. 542, 543.


SECTION IV.--_Of Probabilism_.


1. Sometimes conscience returns a clear, positive answer as to the
morality of an act contemplated. True or false the answer may be, but