[Breadmaster] How about the sense of guilt? Doing something you know to be wrong makes you feel guilty. So, to put it another way, if something makes you feel guilty, it's something you feel to be immoral (this can be irrationally so, of course, insofar as any morality can be said to have a rational basis). Obviously, this isn't objective because different people feel guilt for different things.
[Darren] Ok, one can imagine how to make a lot of money at street crime, but I seriously doubt if anyone does. It's just not a real career option for anyone wanting to do more than just live hand to mouth. [Bm] What is a "should"? What are commands? The moral person would no more thrust his hand into another's pocket than into a nest of vipers. Shoulds and commands are for those who lack insight and must be told what to do. I have not (yet) read Aristotle (is this the Nicomachean Ethics?), but morality as enlightened prudence sounds right to me.
You see - you can prove it, with one of these. You just need to know the wavelength of the light which will tell you where it is on teh spectrum which will (in most cases) be able to be proved to be a certain colour (except for those "No it's yellow" "no it's not it's orange" conversations.)
[st d] Whether you can prove it or not wasn't the point - it was whether you needed to prove it, or indeed whether you even needed to know a proof was possible.