The Source of Morality for the Non-religious

I want to address the problem of being able to measure the morality of
someone who does not purport to hold themselves to a holy writ as a
standard. Some people claim to have "personal moralities," and of course there is secular law, both of
which try in some way to fill the niche of religious moral codes, with
varying degrees of success. Alas, what is legal, what is moral, and what
you can get away with, are three very different things. What you can get
away with is the only "morality" imposed by the world at large, but a
society in which that was the rule would be no society at all.

I can think of at least one main difference between the morality of the religious and the
morality of the non-religious, where here I'm talking about people who
take their religion seriously, not just those whose self-identification
with a religion is href="http://www.philosophy-religion.org/criticism/cultural.htm">more
cultural and social than relgious. The difference is that the morality
of the religionist (at least monotheists) is based on institutions,
traditions, and in particular, on documents which, in theory, can
be agreed upon by all co-religionists of that faith, which serve as a
common basis for their morality. And even non-co-religionists can read
the same documents and measure the standard of the religionists' behavior
against the stated morality of the religion. In other words, there is an
authority to which both the religionist and the non-religionist can refer
with regard to the morality of the religion. This permits one to criticize
a Christian or Muslim, because the moral teachings they supposedly adhere
to are well documented.

I cannot think of a parallel authority for the morality of the
non-religious person. By what measure would his or her conduct be
considered moral? Would his or her conduct be measured against the moral
code of a religion to which he or she does not ascribe? Would it be
measured against the law of the nation in which he or she is a citizen? Or
if not by the law, at least the "traditional" morals of the nation? Would
it be measured against some "universal morality," an invariant subset of
the moralities of all existing cultures and value systems? But
certainly the set of moral prescriptions of this universal morality would
necessarily be small, e.g., don't murder, don't lie, etc. I doubt a
universal morality would be very substantive. Any 'meaty' morality would
have to be a morality composed of morals taken from particular
philosophies or religions.

Would the conduct of a non-religious person be measured against a
personally determined morality? Unless the moral code to which the
non-religious person is trying to live up to is clearly stated somewhere,
I don't see how he or she can claim to be moral. I'm not trying to be a
smart aleck about this. I think it's a very serious issue and it needs an
answer.