The second subsection of Chapter 4 is only two pages long (pp. 57-58), but it deserves our careful attention for several reasons: (i) One reason is Nozick’s geometric visualization of morality. As Nozick puts it (p. 57): “an area in moral space” or moral boundary surrounds every individual. (ii) Another reason is that Nozick raises (yet again!) a fundamental question, an inquiry so important that it will take up the rest of Chapter 4. Specifically, Nozick poses a subtle query about the nature of this geometric moral boundary. Should the moral line surrounding each person be treated as an impenetrable wall — one that others are forbidden to transgress — or merely as a suggestion or default position — a moral line that others are permitted to step over so long as they compensate the person whose moral boundary has been crossed? (Before proceeding, it’s worth noting that this fundamental question must be answered regardless of where this line is drawn, no matter whether you are a pragmatic Humean consequentialist or are committed to universal Kantian duties. Either way, we must also decide what to do when moral “boundary crossings”, to borrow Nozick’s apt metaphor, occur.)

(iii) Yet another reason to pay close attention to pp. 57-58 of Chapter 4 is Nozick’s reciprocal stance towards moral boundary crossings. To borrow Nozick’s own terminology, assume two autonomous individuals, X and Y, and further assume that compensation is required for any border crossing (regardless where we draw the line). Does X have a reciprocal duty to take whatever steps or precautions are prudent in order to reduce the likelihood of Y committing a boundary crossing or to minimize the impact of Y‘s border-crossing once such a violation occurs? For his part, Nozick appears to adopt (at least tentatively) a “reciprocal” view of moral border crossings (p. 58): “We shall tentatively adopt [a reciprocal] view of compensation, one which presumes reasonable precautions and adjusting activities by X.” So, if Y has a moral duty to avoid crossing X‘s moral boundary, then to the extent harms are the product of the actions of both parties (X and Y), X also has a reciprocal moral duty to arrange his affairs so as to reduce the probability of border crossings and to limit his losses when such border crossings do occur.

Although we agree with Nozick that in most cases moral duties are indeed reciprocal — at least to the extent moral (and physical) harms are the product of both parties’ decisions and actions (one of the main lessons of Ronald Coase’s famous paper, “The Problem of Social Cost”) — this reciprocal moral logic is not universally accepted by everyone, least of all by many moral philosophers! Also, we find it very strange that a good Kantian like Nozick (“Individuals have rights …”) would be willing to even consider the possibility of compensation for moral border crossings. After all, doesn’t Nozick’s side-constraint view of morality imply that our moral boundaries should be treated like an impenetrable wall instead of a mere suggestion or default position? To his credit, Nozick will not leave these questions open; he will carefully respond to these potential objections later in the chapter …