Random small essaylet I cam up with after a discussion on Twitter, putting it here for my own reference.
In a recent discussion with someone defending the concept of good as fulfilling a function, the other party agreed with me that something can only be said to have a function at all if it’s part of a system in some sense, whether strict or loose. For instance, we can say a heart fulfills its function well only by considering it part of a system, namely a human body (this is the strict meaning). We can say a watch fulfills its function as a timekeeper well only by considering it a part of a system in a loose sense (part of the working world of humans who need to keep track of time, if humans disappeared the watch would just be a meaningless mechanism).
The other person said that even if fulfilling a function well or poorly is relative in that sense (i.e relative to a system), it’s still objective, because objectivity means being independent of a “valuer,” not being independent of anything at all.
The problem is, if you concede that function is unintelligible without reference to a system, it soon becomes apparent that in human ethics, at the very least, you still need a valuer because human beings are relevantly parts of so many systems.
Take the example of a hardworking employee who spends so much time at the office or factory that he neglects his wife and son. As a part of his workplace—i.e an employment system—he’s fulfilling his function very well, but as a husband and father—i.e part of a system, namely his family—he’s failing. So how do we determine which function is more important for him to fulfill? The more time he spends with his family, the less time he can spend at work, and vice versa. So even if we define goodness as merely fulfilling functions, that definition is of very little use for humans (or really any other complex matters) because humans usually have a broad variety of functions within a broad variety of different contexts, many of which are at odds with each other–unlike the other guy’s initial example of hearts and watches, which each only have one function. So to rationally choose between those competing functions requires a standard of value (i.e one function is more important than another somehow) that itself has nothing to do with fulfilling a function, which is the sort of standard the guy originally wanted to avoid.