Parfit rephrases Kant’s FUL as:
FUL: It is wrong to act on maxims that we could not will to be universal laws. [15: 285]
Parfit’s understanding of FUL differs from Kant’s in that Parfit is sceptical of the idea that it is possible to identify morally bad actions via a conceivability test. He only considers what can be rationally willed as a universal law,Footnote 3 and does not distinguish between maxims that fail the FUL test because they cannot be rationally willed as universal, and those that fail because they cannot even be conceived of as universal. Hence, we do not find in Parfit an equivalent to Kant’s distinction between perfect and imperfect duties (IV: 424). In what follows, we will base our discussion on Parfit’s understanding of FUL.
Parfit considers FUL to be the best candidate of those offered by Kant for a supreme principle of morality. However, Parfit claims that we have to revise the formula to avoid objections. Ultimately, we arrive at a version of the formula that is supposedly compatible with Contractualism:
“An act is wrong unless such acts are permitted by some principle whose universal acceptance everyone could rationally will”. [15: 341]
One important step on the path from FUL to Parfit’s revised version of it is to abandon a certain understanding of maxims: namely, as policies. According to Parfit, there is no problem with a conception of maxims whereby maxims describe one specific action, performed in a specific situation. These maxims would be equivalent to the term “such acts” in the revised formula just cited. According to such a conception, a maxim would list all the morally relevant properties of a specific action and of the specific situation in which the action is performed.
However, Kant himself considers maxims to be policies that can be very general and can abstract from many specific properties of concrete situations. Examples of such maxims include “increase my wealth by every safe means” (V:27) and “let no insult pass unavenged” (V:19). Such maxims are not descriptions of a specific action, since there are many different types of actions in many, very different situations that could be performed under these maxims. The distinction between two understandings of maxims, as action descriptions and as policies, will be crucial for the purposes of our paper. Parfit presents a number of arguments against the notion that maxims, understood as policies, are the proper objects of moral evaluation.Footnote 4 Of these arguments, we will focus on the Mixed Maxims Objection, and discuss other arguments only insofar as they are relevant for a correct understanding of the nature and force of the Mixed Maxims Objection.
Parfit alleges that Kant “overlooks” [15: 293] the fact that maxims can be mixed. “Mixed” here indicates that maxims can be instantiated in both permitted and prohibited actions. When someone follows the egoistic maxim of doing whatever serves their own interests, they might pay their debts, help others, etc. Alternatively, they might steal, cheat, take more than their fair share, etc. When someone follows the maxim of improving their standing in the eyes of others, they might rescue a drowning child, donate to charity, etc. Alternatively, they might lie about their accomplishments, slander others, etc.
Parfit himself contemplates a number of different ways in which the existence of mixed maxims may constitute objections to Kant’s notion of maxims. Before we can have an informed debate about responses to the Mixed Maxims Objection, however, we must clarify exactly what is the most pressing challenge that mixed maxims pose. To this end, we will distinguish in the current section three versions of the Mixed Maxims Objection. According to the first version, FUL fallaciously condemns all actions that are performed on an impermissible maxim (a). The second version concedes that FUL does not fallaciously condemn all actions (in the sense of ‘what the agent is doing’) performed on an impermissible maxim, but in some cases when an agent acts on an impermissible maxim, FUL fallaciously condemns the agent’s ‘doing of it’ (b). According to the third version, the problem of FUL is that it does not allow us to derive any conclusions about the permissibility of actions at all (c). We will briefly show how Kantians can avail themselves of responses to (a) and (b) respectively. Moreover, closer scrutiny of (b) will reveal why it is desirable to hold on to Kant’s notion of maxims. By contrast, (c) poses a fundamental problem for Kant that has not yet been sufficiently addressed by Kantians. We will focus on this version of the Mixed Maxims Objection for the remainder of the paper.
(a) The version of the Mixed Maxims Objection that Parfit himself most frequently employs is based on the assumption that FUL is a principle for evaluating the morality of actions. According to this assumption, FUL implies that any action performed on a maxim that does not pass the universalization test is wrong. The Mixed Maxims Objection is then to be understood as:
“When applied to mixed maxims, Kant’s formulas fail, since these formulas condemn some acts that are clearly permissible or morally required”. [15: 293; see also 16: 296]Footnote 5
In cases like the Egoist who pays their debt on a maxim of egoism, Kant would have to conclude that paying the debt is a wrong action. Such a conclusion, however, is absurd.
This version of the Mixed Maxims Objection draws on the idea of false negatives: Kant’s formulas detect a supposedly immoral action when, according to steadfastly held intuitions, the action is not immoral. This line of arguing is akin to other well-known objections from false positives/negatives against Kant’s formulas.Footnote 6 However, there is an important difference between the Mixed Maxims Objection and standard false positives/negatives objections. The latter usually seek to put pressure on FUL by showing how this formula rules out some intuitively permissible maxims and fails to rule out some intuitively impermissible maxims.Footnote 7 The Mixed Maxims Objection, by contrast, focuses on how intuitively permitted actions turn out to be prohibited according to FUL, if they are performed on maxims that FUL prohibits. This difference is potentially significant, as it implies that, even if standard false positives/negatives objections could be overcome and FUL ruled out all and only intuitively forbidden maxims, it could still be the case that some actions performed on impermissible maxims strike us as morally permissible.
As already mentioned, Parfit’s central assumption is that FUL is a principle for evaluating the morality of actions. A number of philosophers agree with this assumption and also concede that, according to Kant, an action would turn out to be wrong if performed on an impermissible maxim.Footnote 8 However, many Kantians, such as Thomas Pogge  and Sven Nyholm , believe that FUL is not supposed to say anything directly about the morality of actions. Instead, as Kant himself presents FUL (“act only according to that maxim …” IV:421) and frequently applies it to examples (e.g. IV:421-3), FUL is concerned with principles of actions or maxims and does not pertain directly to the moral status of individual actions. According to this reading, although FUL states that it is wrong to act on impermissible maxims, it does not imply that every action performed on an impermissible maxim is a wrong action, as FUL is not concerned with actions.
Parfit is right to argue that FUL would lead to implausible results if it is understood as a principle for the evaluation of actions. However, since there is an alternative reading of FUL that avoids these implausible results, and since this reading is also the one that Kant himself seems to have in mind, we should follow that alternative reading. Moreover, it is worth highlighting the fact that Parfit’s wording of FUL does not support the version of the Mixed Maxims Objection that Parfit himself most frequently employs, as he maintains that “[i]t is wrong to act on maxims that we could not will to be universal laws” [15: 285]. However, the wrongness of acting on certain maxims does not imply the wrongness of all actions performed on these maxims.
Thus, the first and perhaps most straightforward understanding of the Mixed Maxims Objection is not the strongest version of it, as it presupposes an unconvincing interpretation of the role of FUL. This has led a number of philosophers to conclude that the Mixed Maxims Objection as a whole is simply based on a misunderstanding [10: 286, 17]. As we will see, however, this is not the case.
(b) Parfit himself is aware that some Kantians have a different take on FUL. He therefore emphasizes that the problem of mixed maxims reoccurs as a matter of fact even if we grant that FUL is supposed to evaluate not an action but rather what Parfit calls an agent’s “doing of it” [15: 290f.].Footnote 9 Hence, the second version of the Mixed Maxims Objection states that, in some cases, FUL wrongly condemns some innocent ‘doings of it’. A closer look at this version will, pace Parfit’s own intentions, illuminate why maxims should be seen as morally relevant after all.
Parfit introduces the idea that Kant distinguishes between the statements “what [an agent] is doing is wrong” and “his doing of it is [wrong]” [15: 290]. The former refers to the action itself, and the latter to how someone is acting in a broader sense, including their motivation and underlying attitudes. According to this distinction, when someone helps a friend out of egoistic motivation, ‘what the agent is doing’ (helping a friend) might not be wrong, but the agent’s ‘doing of it’ (acting egoistically instead of acting from duty) is wrong. At first glance, it seems that the Mixed Maxims Objection misfires if we understand FUL as making statements about the agent’s ‘doing of it’ because Kant could agree that there is a real sense in which helping a friend is not wrong even if the agent is acting on an impermissible maxim (if their ‘doing of it’ is wrong).
However, Parfit believes that this distinction does not solve the problems that mixed maxims pose. According to Parfit, even if we understand FUL as making claims about the agent’s ‘doing of it’, FUL still yields many false verdicts, since impermissible maxims may correspond to clearly permissible ways of the agent’s ‘doing of it’. According to that understanding, the Mixed Maxims Objection could now be stated as:
Kant’s formulas fail, as these formulas condemn some ‘doings of it’ that are clearly permissible or morally required.
Unlike the first version, this second version of the Mixed Maxims Objection is in line with Parfit’s own wording of FUL as it pertains to acting on maxims as opposed to actions (“[i]t is wrong to act on maxims …”). The second version of the Mixed Maxims Objection again resembles a version of the objections based on false positives/negatives, although the false verdicts that the formula supposedly issues pertain to the agent’s ‘doing of it’ (the way they are acting).
Parfit offers several paradigmatic scenarios for maxims that, while impermissible according to FUL, nonetheless correspond to intuitively permissible ‘doings of it’. We will discuss two of these here as, pace Parfit, they illustrate why we should hold on to the notion of maxims in Kant’s sense. Both scenarios refer to situations in which agents do not have moral duties. Parfit assumes [15: 290] that if there is no moral duty, then there is no demand for a specific ‘doing of it’, and, in particular, there is no demand to act from the right motive. The first paradigmatic scenario features an agent who performs prudent actions that do not affect anyone else. If somebody performs a prudent, self-oriented action on an impermissible maxim, then it seems that they do not violate the demand to act from duty because there is no duty pertaining to this situation. Hence, there is no sense in which they are acting wrongly, or so one might think.Footnote 10 However, FUL implies that they are in fact acting wrongly.
“When this Egoist takes some medicine, or puts on warmer clothing, he may be acting on his maxim ‘Do whatever would be best for me’. Since this man could not will that this maxim be universal, Kant’s formulas again mistakenly imply that he is acting wrongly. Nor could we claim that, though what he is doing is not wrong, his doing of it is. There is no sense in which, when this man puts on warmer clothing, his acting in this way is wrong.” [15: 291]
The second scenario is a situation in which there is no moral duty, yet certain options would be considered supererogatory. Suppose a child has fallen into a fast-flowing river, and rescuing the child would be too risky to be morally required. Nonetheless, a man jumps into the water and rescues the child, acting on the maxim of maximizing the prospect of reward. Again, according to Parfit, there would be no sense in claiming that the man’s doing of this is wrong:
“On the suggestion we are now considering, if this man saves this child’s life at this great risk to his own life, what he is doing is not wrong, but his doing of it is. That is clearly false. This man is not failing to fulfil any duty, or acting wrongly in any sense.” [15: 291]
However, let us look critically at these two examples in turn. Contrary to what Parfit believes, there is a sense in which, although the Egoist who takes the medicine does not perform an impermissible action, they fail to act in the right way. After all, it is only contingently the case that taking the medicine on the maxim of egoism does not harm anyone. Suppose the situation changes: someone enters the room and informs the Egoist that all of the remaining medicine is needed for a third party who faces imminent death. In that case, the Egoist, following their maxim of unlimited egoism, would nonetheless take the medicine, accepting the risk of death to the third party, even if their own life was not endangered and the medicine would merely cure their cold. Suppose now that there is, in fact, no third party facing death and, consequently, no one tells the Egoist that the medicine is needed elsewhere. Nevertheless, the Egoist’s acting is in this case defective and, in an important sense, morally wrong, because of their disposition to allow others to die if this were a side effect of their action. That is why there is something wrong with their ‘doing of it’ and, hence, FUL does give us the correct verdict.
Similarly, the man standing by the fast-flowing river is disposed not to rescue the child: he would not save the child unless there were a realistic prospect of reward for doing so. As Parfit describes the case, there is no duty to rescue the child (whereas, in the medicine case, there is a duty not to deprive the hypothetical third party of the much-needed medicine). However, we think that the rescuer’s acting is not beyond criticism, because, under different circumstances, the man would have performed actions that were clearly morally wrong. For instance, following his maxim of maximizing the prospect of reward, he would have thrown the child into the river if this would have created a situation that holds out the prospect of reward. Even if the man saved the child, his acting is defective because he acts on a maxim that would lead him to commit immoral actions in other situations.
One might object here on the grounds that it seems as if we are suggesting that the rescuer should relinquish his defective maxim of maximizing the prospect of reward. However, if he did that, then he might no longer be willing to jump into the water to save the child. This would mean that, paradoxically, a person who is morally better than the man looking for reward might not rescue the child. However, this line of reasoning is misleading as the would-be rescuer is not obliged to relinquish his maxim entirely, but simply to condition it. If he changed the maxim “Do whatever maximizes the prospect of reward!” to the maxim “Seek reward as long as you are not violating the rights of others!”, then he would not throw the child into the river, but would still rescue the drowning child to obtain reward.
In summary, Parfit’s attempt to demonstrate that a version of the Mixed Maxims Objection reoccurs even if we assume that there is a distinction between the wrongness of what an agent does on the one hand, and the wrongness of their ‘doing of it’ on the other, is unconvincing. In contrast, our discussion of Parfit’s examples that were supposed to illustrate this new version of the Mixed Maxims Objection suggests that acting on a permissible maxim is part of a permissible ‘doing of it’. In fact, a closer look at Parfit’s examples reveals that FUL gives us correct answers because evaluating maxims is an important element of moral reasoning, an element that we should hold on to and that Kantian ethics rightly places great emphasis on. Suppose the Egoist never committed a moral wrong such as pushing a child into a river and undergoes a moral conversion later in life. They might plausibly feel remorse when remembering situations in which they were willing and prepared to push a child into a river if they had been certain it would have been in their self-interest. In this scenario, the Egoist feels remorse not for their actions, having never actually pushed a child into a river, but for the person they were or for the priority that they accorded their self-interest.
Barbara Herman, in her critical reply to Parfit in the second volume of On What Matters, draws on a similar example to expose the shortcomings of Parfit’s departure from Kant [6: 87-89]: a gangster feels remorse after a moral conversion not just for their actions, but for the person they were and for the actions they could easily have performed. The gangster was a person who did not respect the rights and moral status of others, and who acted based on wrong attitudes towards their fellow human beings. Herman argues that Parfit’s theory, with its focus on actions as opposed to maxims and character, cannot account for cases where agents regret things that they might (easily) have done to others, given the person that they were at the time. Providing a framework to evaluate dispositions or priorities is a desideratum for ethics as it can capture the significance of counterfactual self-evaluation and feelings of remorse for one’s attitudes and character.Footnote 11 Parfit wrongly neglects the moral importance of such dispositions.Footnote 12
(c) Notwithstanding our argument so far, the Mixed Maxims Objection can be formulated such that it constitutes an even more pressing challenge to FUL. The problem revealed by the existence of mixed maxims might not be that FUL gives false verdicts about actions, but that it gives no answers concerning the morality of actions at all. We can state the revised version of the Mixed Maxims Objection as:
One of the central tasks of ethics is to answer the question of which actions are morally permissible. If there are mixed maxims, then the evaluation of maxims is of no relevance for this central task, as maxims do not reveal anything about the permissibility of actions.
The idea that one crucial question of ethics is concerned with the moral status of actions constitutes a general challenge to an ethics of maxims. This challenge is not limited to the problem of mixed maxims, as there are other potential gaps between the evaluation of actions and maxims that might leave an ethics of maxims unable to say anything meaningful about the morality of actions. For instance, it could be the case that maxims are so abstract and general that they leave underdetermined which actions can be performed on them. It might therefore be impossible to evaluate every possible action, even if we could avail ourselves of a principle that infallibly evaluates maxims. However, mixed maxims are the most immediate and pressing challenge for an ethics of maxims, since, if there are mixed maxims, it seems that we cannot transition from the (im)permissibility of maxims to the (im)permissibility of actions. After all, any maxim could in principle be a mixed maxim. It then falls to the Kantian to show that the evaluation of maxims can indeed inform our evaluation of the morality of actions. We should note that the problem that FUL might say nothing about the wrongness of actions might be even worse than false negatives. It would mean that FUL missed one of the central points of ethics, and not that it is a deficient or less than ideal answer to the question of how we are to act.