I looked at Parfit's discussion of the requirements of Kant's Formula of Universal Law (FUL) in Climbing the Mountain recently and in this posting I am going to look at some of the salient features of his treatment of it in the 2008 version of On What Matters. Whilst the treatment here is in some respects continuous with that in Climbing the Mountain I want to use the review of it to assess some of the ways the requirements of the test of maxims based on FUL are understood by Parfit and how this understanding relates to other views in the secondary literature on Kant. I will refrain, in this posting, from replying to these conceptions except to mention the reasons why Parfit rejects a number of such interpretations.
As in the previous treatments of the topic so here Parfit opens by viewing one way of assessing the requirement of FUL as stating what he terms an "impossibility formula" so that what cannot be willed is something we could not take to state a universal law. However, whilst this generally does capture part of what seems to be involved in the contradiction tests that are related by writers to Kant's FUL, Parfit takes it that we need a further refinement of the "impossibility formula" before we can describe it as indicating what kinds of action are "permissible". It is not, says Parfit, that Kant refers to maxims that we could not all be permitted to act upon simpliciter. Nor does Parfit think that permissibility should be understood in terms of maxims that all could "accept" since "acceptance" alone seems to him too neutral a term. Similarly Parfit does not think permissibility can be understood in terms of what "everyone" could act upon since many maxims have particularistic content but of a sort that is demonstrably referring to moral concepts. More generally referred to is a way of viewing permissibility that refers us to actions that could be "successfully" acted on, a notion that many writers have tried to view FUL in terms of but which Parfit rightly rejects as generating false negatives.
Having gone through all these ways of looking at FUL Parfit replaces the initial formulation of it to one that incorporates, oddly enough, the reference to "success" that he has previously rejected as a way of interpreting "permissibility" and assesses some maxims in reference to this revised requirement but, unsurprisingly, finds the results discouraging. The revised formula does not, says Parfit, "condemn self-interested killing, injuring, coercing, lying, and stealing". Assuming this is so it is reasonable to wonder why Parfit spent time considering a revised formula that he had already found reason to reject? One reason appears to be that Kant's paradigm example of lying promises could be rejected by reference to the "success" understanding of "permissibility". Having located this result Parfit next revises again the understanding of the "permissibility" interpretation of practical impossibility to read: "It is wrong to act on any maxim of which it is true that, if everyone believed such acts to be permissible, that would make it impossible for any such act to succeed".
However the problem Parfit next raises concerns the types of practices to which the formula as given should be attached stating that the undermining of promises would involve the destruction of a valuable set of practices but adding now that it is not only to valuable practices that the formula would have to be applied. Counter-examples are marshalled now both to the idea that it is universally true that promising is a valuable social practice and to the idea that the formula only picks out social practices that possess value. The result is, once again, that the formula has mixed results, condemning some acts that we would usually take to be right and, furthermore, when it correctly condemns acts, doing so for a reason that does not appear to Parfit, at least, to be good.
Still staying with a variant of the interpretation of the practical impossibility requirement that sees this in terms of some reference to "success" Parfit next looks at a version of the formula that would describe wrong action as based on a maxim that would, if universally acted on, "make it impossible for anyone successfully to act upon it". This formula is often described as preventing action on maxims that we normally think people should act upon such as giving generously to the poor. Whilst Parfit concedes that Christine Korsgaard has a partial reply to this objection he still presses a restricted version of it and, furthermore, points to other maxims that are not affected by Korsgaard's defence. Onora O'Neill has similarly pressed a version of the "success" conception that Parfit rejects on familiar grounds concerning false positives and false negatives. The more restricted sense of the "success" criterion views it in terms of some acting on maxims whose success depends on their being exceptional (a variant proposed by Korsgaard) but which runs into trouble with common examples such as aiming to use tennis courts at unpopular times. This leads Parfit to reach a summary conclusion of the different attempts to rescue the practical impossibility view of FUL and to say that "none contains a good idea".
Having rejected thus summarily all the versions of the practical impossibility view of FUL Parfit looks next at the way Kant himself phrases it in terms of willing. The reference to willing is, however, understood by Parfit to bring in its wake Kantian thought-experiments concerning possible worlds. It is with regard to such that Parfit understands the claims about consistent willing and avoidance of contradiction. However, added to these notions is Parfit's own conception of "rational" willing. As Parfit puts this: "for our choices to be rational, we must also respond well to reasons or apparent reasons". In so doing what we have to take account of, on Parfit's view, are "facts that give us clearly decisive reasons".
The turn to viewing things through the prism of thought-experiments is clearly grist to the general mill of Parfit's own conceptions and it is at this point, unsurprisingly, that Parfit turns away from FUL strictly speaking to the schematised form of it that Kant presents in both the Groundwork and the Critique of Practical Reason, namely, the "law of nature formula", a formula interpreted by Parfit to include his conception of rational willing. It is after reaching this point that Parfit's interpretation becomes truly inventive. Parfit suggests that Kant often applies FUL not necessarily simply by reference to the law of nature but also by introducing other supplementary ideas. One of these is "permissibility" interpreted now not in terms of "impossibility" as previously but rather simply expressed as a requirement in its own right: "It is wrong for us to act on some maxim unless we could rationally will it to be true that everyone is morally permitted to act on this maxim". The application of this formula is seen by Parfit as affecting what people would be likely to do but having seen the formula in this way he also indicates it in fact introduces an epistemic constraint on people. This leads to the formulation of what Parfit terms "the Moral Belief Formula" and MBF is stated as follows: "It is wrong for us to act on some maxim unless we could rationally will it to be true that everyone believes that such acts are morally permitted". Not only is this epistemic constraint introduced but Parfit assumes it presents a better understanding of permissibility than can be gained by the permissibility formula alone.
The introduction of MBF is taken by Parfit to underlie questions often attributed to Kant such as the famous "what if everyone did that" notion. If questions are to be assessed however that really concern beliefs the question is how such beliefs are to be framed. Parfit assumes that if we appeal directly to deontic beliefs or deontic reasons the appeal to Kant's notion of universal laws would be pointless since we would simply be building moral requirements into our criteria when the criteria is supposed to be determining them. This point is expressed by Parfit as a "deontic beliefs restriction".
Having arrived at this point Parfit steps back from where his argument has proceeded up to this point and introduces another element into his discussion. This element concerns the way the maxims we are testing are to be understood and Parfit indicates that he takes maxims to express policies of agents. The problems that then arise in relation to the universal test of maxims are stated in terms of agential conceptions. This occurs through stating the requirement of universality in terms of permissibility which is then presented with the problem of highly specific maxims. This problem is stated in terms of what Parfit calls the "rarity objection". Parfit accepts that this objection is at least partially one Kant can respond to as people do not themselves tend to state the basis of their conduct in terms of such highly specific maxims. But this is only taken to be a partial reply since there is nothing inconceivable in principle in the existence of such people.
The next problem that Parfit introduces is different in scope. It occurs through the introduction of the figure of the egoist acting on the general (not highly specific) maxim of doing what best serves their interest. In this case, Parfit argues, the figure in question can perform acts that in themselves seem fine but which are apparently rejected tout court simply because of his adherence to a generic maxim that is always rejected. This implies wrong acts are occurring when independent of the application of the criteria of universalisation we would not normally think so. This leads Parfit to introduce the notion of "mixed maxims", mixed in the moral sense that sometimes action in accordance with them would be wrong and sometimes right (where wrong and right are clearly conceived in terms of outcomes). This objection by reference to mixed maxims is then added to the "rarity objection" to produce what appears to be a general argument on Parfit's part against recourse to universalisation tests.
There have been a few philosophers who work in the general area of Kantian ethics who have followed similar reasoning to reach a similar result and thus rejected the idea that Kant has provided a universalisation test really. Barbara Herman, for example, moved away from this way of looking at Kant's references to universalisation towards the general notion of "deliberative" or rebuttable "presumptions" built into the practice of moral judgment. Onora O'Neill, by contrast, seems to take the discussion of universalisation to produce results not concerned with wrong-making characteristics of actions but instead as descriptive of actions that have moral worth.
However Parfit does not follow the suggestions of Herman and O'Neill. Instead Parfit refers to Kant's discussions of actions in conformity with duty in order to indicate that Kant had a broader notion at work in his recourse to universalisation than the modest conception some Kantian writers have suggested. In setting out this broader notion Parfit refers back first to the "mixed maxims" objection and argues that, in considering it, we need to know "all of the morally relevant facts". This point is part of the reason, according to Parfit, why Kant often discusses maxims in terms of underlying policies though this alone is not taken by Parfit to be sufficient for knowing all the "moral facts" that are relevant. Not only is this so but Parfit rejects reference to "policies" altogether as including information that is often irrelevant to assessment of a situation.
Having reached the conclusion that we should not understand the reference to the law of nature in terms of policies of action Parfit reformulates the universal law formula now in the following way: "We act wrongly unless what we are doing is something that we could have done while acting on some maxim on which we could rationally will everyone to act". This revised formula is said to avoid the "mixed maxims" objection as the action now allows us to call many acts of the egoist right as we don't appeal to his underlying maxim now to judge of his acts. But whilst this revised version gives response to the "mixed maxims" objection, it does not, for Parfit, allow response to the "rarity objection". Rare actions, or ones based on highly specific maxims, could still be allowed on this revised formula.
Due to this a further revision of the law of nature formula is carried out that refers instead to "similar circumstances" and this produces a correlative alteration in the way the epistemic constraint formulated in the moral belief formula is framed. These revised formulas avoid the "mixed maxims" objections but also allow us to avoid the "rarity objection". However, Parfit, having moved away from recourse to underlying policies as a way of assessing maxims now introduces instead of these an account of the "intentions" of agents. This point is one that is not as naive as it initially sounds since Parfit does not assess "intentions" simply as what someone says they wish to achieve. Parfit recognises this point by means of the same example Sidgwick uses at one point when stating that someone blowing up a train on which the Czar was travelling may not "intend" to kill the other passengers but such other killing is nonetheless an intentional part of the action in question. So reference to agent's intentions is not simply stating what they take themselves to be doing but what is built into the action.
Essentially the result of these considerations is that Parfit now revises the understanding of Kant's formulas in such a way as to remove reference to "maxims" altogether although it is far from obvious that this is the way he has to understand his revisions. The sense of "intentional action" may well be the right way to capture the notion of "maxim" and it has, in any case, proved difficult to stabilise what a "maxim" is without reference to considerations that clearly go beyond what is normally taken to be the "intentions" expressed by someone acting. Further, as Parfit discusses, the notion of a maxim does include some sense of subjective principles of action and without it one may wonder what discussion of universalisation is going to be about. Parfit incorporates a response to this question into his next revision of the epistemic constraint specifying this latter in terms of "moral principles" that permit acts.