This is an old post from the Powerblogs site, written a few years ago. The points made still seem correct.
Peter Lupu's version of the logical argument from evil (LAFE) is committed to a principle that I formulate as follows:
P. Necessarily, agent A ought to X iff A is morally obligated to X.
This principle initially appealed to me, but then I came to the conclusion (with the help of the enigmatic Phil Philologos or was it Seldom Seen Slim?) that the biconditional (P) is correct only in the right-to-left direction. That is, I came to the view that there are moral uses of 'ought' that do not impute moral obligations. But so far I have not convinced Peter. So now I will try a new argument, one that explores the connection between the obligatory-supererogatory distinction and the thesis that there are two moral senses of 'ought.' Here is the gist of the argument:
2. Whatever is good to do ought to be done
3. There are two moral senses of 'ought,' one prescriptive the other commendatory.
Ad (1). I am using 'supererogatory' in a wide sense. Accordingly, an action can be supererogatory (roughly: above and beyond the call of duty) even if it is not heroic or particularly costly (financially or otherwise) to the agent. It can be something as trifling as leaving a 50% tip in a restaurant. (Not that hard to do given dives I frequent.) If an action is obligatory, then it is good to do, and bad to leave undone. If an action is supererogatory, then it is good to do, but NOT bad to leave undone. Suppose I have lunch in a restaurant in which the food is good and the service adequate. Then
a. I am legally and morally obligated to pay the bill.
b. I am morally but not legally obligated to leave a 15% tip. (Or so I would argue.)
c. I am neither legally nor morally obligated to leave a 50% tip.
Nevertheless it is a good thing to leave a large tip (other things being equal), but not bad if I fail to leave a large tip. So the action is supererogatory in the wide sense here in play.
Ad (2). The principle that whatever is good to do ought to be done is theoretically attractive. It is attractive because it forges a partial link between the axiological and the deontic which are two aspects of the normative. Axiological terms include 'good,' 'evil',' 'value,' 'disvalue,' 'ideal.' Deontic terms include 'obligation,' 'prohibition,' 'permission,' 'right,' 'duty.'
Note the difference between (2) and
4. Whatever is good ought to be done.
(2) is about the good-to-do; (4) is about the good-to-be, which is a wider category. (4) says that everything which would be good were it to exist ought to be brought about by someone. It suffices to refute (4) to adduce a state of affairs that would be good if realized, but is not in the power of any finite agent to realize. Well, it would be good if none of us had to to die; but the immortality of human beings is not a state of affairs that can be brought about by any finite agent or agents.
Much more needs to be said about the principle (2) but let's assume that one accepts it.
Now under what conditions can it be true both that (1) there are supererogatory actions, and (2) whatever is good to do ought to be done? On the face of it, these seem contradictory. The supererogatory is that which it is good to do but not obligatory. But if what is good to do ought to be done, then it seems to follow that what is good to do is obligatory — which contradicts (1).
The contradiction is avoided if we distinguish between two moral senses of 'ought.' In the prescriptive sense, what one ought to do is what one is obligated to do. In the commendatory sense, what one ought to do is good to do but not obligatory.
But are there any sentences that feature moral uses of 'ought' that do not impute obligations? Suppose my wife says to me, 'We ought to give more of our income to charity.' Suppose further that there is an obligatory percentage and that we are already giving that percentage. In saying what she says, my wife is not imputing an obligation to us; she is recommending that we do more than we are obligated to do. Since the context is moral, this seems to be a moral use of 'ought' that does not impute an obligation. This seems to be a clear counterexample to (P) above.
Suppose instead she had said to me, 'We ought to check out the Roy Orbison exhibit at the Tempe Center for the Arts before it is too late.' Visiting such an exhibit is a morally indifferent action: neither prohibited, nor obligatory, nor supererogatory. The use of 'ought' in this example is nonmoral. It like the 'ought' in 'If you want to get to Tempe from Gold Canyon by freeway, then you ought to head east on the Superstition Freeway.'
Robert Merrihew Adams (Finite and Infinite Goods, Oxford 1999, p. 235) offers this example: "The religious leaders of the world ought to launch an appeal to protect the physical environment in which humanity must live." Someone who says this is not saying that the leaders are under an obligation; he is saying that it would be a good idea were they to act as recommended.
To sum up. There are nonmoral and moral uses of 'ought,' but not every moral use is an obligation-imputing use. So the biconditional (P) is false. What is true is the conditional,
P*. If agent A is morally obligated to X, then A ought to X.