In The Virtue of Selfishness, Ayn Rand writes:

No philosopher has given a rational, objectively demonstrable, scientific answer to the question of why man needs a code of values.  So long as that question remained unanswered, no rational, scientific, objective code of ethics could be discovered or defined.  The greatest of all philosophers, Aristotle, did not regard ethics as an exact science; he based his ethical system on observations of what the noble and wise men of his time chose to do, leaving unanswered the questions of: why they chose to do it and why he evaluated them as noble and wise.

Suppose every one of these sentences were correct.  Wouldn’t this imply that until she constructed her arguments, no one knew the difference between right and wrong?  When Rand loyalist Harry Binswanger spoke at Berkeley in the early nineties, I asked him this very question.  He hastily denied it, but on Rand’s premises, there wasn’t much he could say.  If moral conclusions require logically sound arguments, and Rand was the first philosopher to produce such arguments for moral conclusions, then until she came along, moral knowledge did not exist. 

By itself, the non-existence of moral knowledge does not imply the non-existence of moral (or immoral) behavior.  However, Rand also accepted a common-sense distinction between “errors of knowledge” and “breaches of morality”:

An error of knowledge is not a moral flaw, provided you are willing
to correct it; only a mystic would judge human beings by the standard of an
impossible, automatic omniscience. But a breach of morality is the conscious
choice of an action you know to be evil, or a willful evasion of knowledge, a
suspension of sight and of thought. That which you do not know, is not a moral
charge against you; but that which you refuse to know, is an account of infamy
growing in your soul.

When you snap the two views together, they actually imply that pre-Rand, no one ever “breached morality.”  After all, if no moral knowledge exists, no one can choose an action they “know to be evil.” 

It’s tempting to blame these bizarre implications on Rand’s philosophical ineptitude, but that’s hardly fair.  Her positions on these two issues are uncharacteristically conventional.  I’ve heard many flavors of amateur and professional philosophers insist that, “Moral conclusions require an argument.”  Then they either admit that they don’t have an argument, or defend some bizarre argument that no more than five people on earth are able to explain.  If the reason why “murder is wrong” is that it violates the Categorical Imperative, then it follows that (a) before the Categorical Imperative was discovered, no one knew that murder was wrong, and (b) the vast majority of people who never have and never will understand the Categorical Imperative still don’t know that murder is wrong.

Bizarrely, then, the “no moral knowledge without arguments” position almost ends in historical relativism.  Everyone who died before the wide release of the “proof” gets a pass, no matter how monstrous their actions: “Back in those days, no one knew that mass murder was wrong!  How can you blame me?  I’m no philosopher!”

What alternative is there?  Ethical intuitionism – the view that some moral premises are obvious on their face, and therefore require no proof.  On this view, not only does moral knowledge predate professional philosophers; truisms like “murder is wrong” have been independently discovered countless times.  This doesn’t mean that moral arguments never lead to new moral knowledge; in fact, I think that Rand’s unofficial moral arguments do just that.  But the point of moral argument is to build on the obvious, not prove what every decent person already knows.