I have been saying this for quite some time. I regret not posting it first. It would be nice to have a more formal proof of all of this with utility functions, deontics and whatnot. If you are up for it, let me know. I could help, feedback, or we could work together. Perhaps someone else has done it already. It has always struck me as pretty obvious, but this is the first time I've seen stated like this.
Check out the previous discussion Luke linked to: http://lesswrong.com/lw/c45/almost_every_moral_theory_can_be_represented_by_a/
It seems there's some question about whether you can phrase deontological rules consequentially-- to make this more formal that needs to be settled. My first thought is that the formal version of this would say something along the lines of "you can achieve an outcome that differs by only X%, with a translation function that takes rules and spits out a utility function, which is only polynomially larger." It's not clear t...
I have previously been saying things like "consequentialism is obviously correct". But it occurred to me that this was gibberish this morning.
I maintain that, for any consequentialist goal, you can construct a set of deontological rules which will achieve approximately the same outcome. The more fidelity you require, the more rules you'll have to make (so of course it's only isomorphic in the limit).
Similarly, for any given deontological system, one can construct a set of virtues which will cause the same behavior (e.g., "don't murder" becomes "it is virtuous to be the sort of person who doesn't murder")
The opposite is also true. Given a virtue ethics system, one can construct deontological rules which will cause the same things to happen. And given deontological rules, it's easy to get a consequentialist system by predicting what the rules will cause to happen and then calling that your desired outcome.
Given that you can phrase your desired (outcome, virtues, rules) in any system, it's really silly to argue about which system is the "correct" one.
Instead, recognize that some ethical systems are better for some tasks. Want to compute actions given limited computation? Better use deontological rules or maybe virtue ethics. Want to plan a society that makes everyone "happy" for some value of "happy"? Better use consequentialist reasoning.
Last thought: none of the three frameworks actually gives any insight into morality. Deontology leaves the question of "what rules?", virtue ethics leaves the question of "what virtues?", and consequentialism leaves the question of "what outcome?". The hard part of ethics is answering those questions.
(ducks before accusations of misusing "isomorphic")