First, a little explanation of NNL. NNL derives specific moral/practical norms by positing two things:
- (1) A set of basic goods--things that are intrinsically good/valuable/worthwhile for humans to pursue. So, they are always "worthy of pursuit." In other words, they are always "to-be-pursued." Also, the basic goods can make immediately intelligible one's action, and are thus reasons for action. This is very important: The basic goods are the fundamental reasons for action; the fundamental "building blocks" of practical rationality. Examples include knowledge, life, friendship, aesthetic experience, and excellence in play.
Let's consider an example. For instance, suppose you ask me, "Why are you running?" and I say, "To help my heart get stronger," to which you reply, "Why do you want to make your heart stronger?" If my answer is, "For the sake of my health, that I might live and live to the full," then this is a "question-stopper;" you can immediately see why I might want to do this, and thus health is a reason for acting that makes my action immediately intelligible; it immediately "make sense." This is because acting for the sake of someone's health is intrinsically valuable and worth doing.
This is the first part of NNL: There is a set of basic goods, as defined above.
- (2) A set of principles of practical reasonableness--these are principles or rules that tell us how it is reasonable to respond to instances of the basic goods. Examples include the golden rule, the prohibition against directly intending to harm a basic good for the sake of something else, rules against arbitrarily discriminating against the goods of certain people, the rule of being reasonably efficient in how one pursues one's plans, etc.
Much more needs to be said here obviously. Many books have been written. However, I don't need to get too much into the details of this for the sake of my post here. That's just the basic idea.
Now, one of the ideas about the basic goods that motivates some of the principles of practical reasonableness is the incommensurability thesis. Here is the thesis of incommensurability:
- (INC) For each basic good x, it is not the case that x offers all the goodness ("to-be-pursuedness") of some other basic good and more.
Now, the motivation for the incommensurability thesis, as I've stated it, is that it seems that each good is beneficial to humans in a way which none of the other goods is. It has a unique type of goodness. Health is good for us in a way that knowledge is not, which is good for us in a way that friendship is not, and so on. If on the other hand we supposed the contrary of incommensurability, then some basic good x would offer all the goodness and more of some other basic good, say y. But then it's hard to see how y could make one's action immediately intelligible (which is part of the definition of a basic good). After all, if someone says, "I did this action for the sake of y," then in some circumstances you can reasonably say, "Well, you should have acted for the sake of x instead, since it offers all the goodness and more of y. So why didn't you?" In which case y would not be a basic good, since acting for the sake of y should make one's action immediately intelligible, and in this case it doesn't. But that's a contradiction, since we assumed y is a basic good. So the incommensurability thesis is true.
Now, one objection is that it seems we should be able to prioritize the goods. Religion is more important than life, life is more important than knowledge, knowledge is more important than fun, and so on. This seems plausible to some. But, if NNL is right, none of these can be "weighed" against the others, since none of them offers all the goodness of any of the others and more. So, the objection goes, if incommensurability holds, then we can't prioritize the goods.