Tacoface:
Here is the best critique of natural-law I am aware of in libertarian literature:
If you haven’t read O’Neil’s article, it is probably required reading for anyone interested in natural law, pro or con.
Here is one of the key passages on page 94/95:
(apologies to those who have seen this before)
"…let us assume thatthe ultimate value of a particular ethical system could he proven,
what could be made of conscious, deliberate defiance of it?
We come upon a man committing some act grossly violative of his nature: let
us say that he was engaged in a theft. We apprehend him, and while we have him
in custody we question him about the nature of the act we caught him performing.
We fmd he is an extremely knowledgeable fellow, familiar with all the arguments
of the natural law school. In fact, he has read Rasmussen’s article and was con-
vinced that the proposition that a man ought to act in accord with his nature is
correct, logically. “Well,” we ask him, “if you know that to steal is to act against
your nature, and you know that you ought to act according to your nature, how
could you bring yourself to commit your felonious act?” “I chose not to act in
accord with correct ethical principles,” our philosophical burglar might answer.
My story, I trust, illustrates the problem. To deny an ultimate value and to
defy an ultimate value are not at all the same activity, and it is the latter which
provides the stronger suppolt of the is-ought dichotomy. One can deny a fact, but
one cannot defy one. You can deny the law of gravity is operative in the world,
but your denial will have no effect on what will happen when you step off a
precipice. The law of gravity operates no matter which course of action you
pursue-if you accept the existence of the operation of the law and hold yourself
back from the edge of the cliff, or if you reject the truth of the law of gravity
and step over the ledge, or if you accept the truth of the law, but wish to fall (let
us say as a means of suicide), in all three cases the operation of the law of gravity
is unaffected.
Moral law does not work in this way, however. One can admit the intellectual
correctness of a proposition of moral law (even of its ultimate value), and yet
deliberately defy it. This being the case, we must question what moral law means:
If one could not, by any means whatsoever, defy moral law, great difficulty would
arise over the appropriateness of the use of “ought”-for we do not normally use
that word to command actions which in any event cannot be avoided. If, on the
other hand, one can and does defy the imperative of a moral law, how is one still
seen as bound by it? Punishment or other ill consequences do not suffice to make
moral law objective, for if the person committing the violation of the maxim(s)
prefers the object of his illicit action, even when coupled with punitive or other
unfortunate consequences, that seems to mean that there is no apparent reason why
he should not act contrary to that moral law.
Any reason offered for why one should not act contrary to moral law must
either be a fact or a value. If a fact, it will need to he made relevant by the accep-
tance (envaluation; not epistemological acceptance) of that fact by the individual’s
will, which condition, in turn, renders it subjective. If a value, it, in its turn, will
require an answer why it may not be defied, and so ad injnitum."