A theory of Justice: Revised Edition

parties.
27
The crucial question here, however, is whether the principles of justice
are closer to the tendency of evolution than the principle of utility. Off-
hand it would seem that if selection is always of individuals and of their
genetic lines, and if the capacity for the various forms of moral behavior
25. Ibid., ch. V, pars. 16–25.
26. See Konrad Lorenz, his introduction to Darwin’s 
The Expression of the Emotions in Man and
Animals
(Chicago, University of Chicago Press, 1965), pp. xii–xiii.
27. Biologists do not always distinguish between altruism and other kinds of moral conduct.
Frequently behavior is classified as either altruistic or egoistic. Not so, however, R. B. Trivers
in “Evolution of Reciprocal Altruism,” 
Quarterly Review of Biology,
vol. 46 (1971). He draws a
distinction between altruism and reciprocal altruism (or what I should prefer to call simply reciproc-
ity). The latter is the biological analogue of the cooperative virtues of fairness and good faith. Trivers
discusses the natural conditions and selective advantages of reciprocity and the capacities that sustain
it. See also G. C. Williams, 
Adaptation and Natural Selection
(Princeton, Princeton University Press,
1966), pp. 93–96, 113, 195–197, 247. For a discussion of mutualism between species, see Irenäus
Eibl-Eibesfeldt, 
Ethology,
trans. Erich Klinghammer (New York, Holt, Rinehart and Winston, 1970),
pp. 146f, 292–302.
440
The Sense of Justice

---

has some genetic basis, then altruism in the strict sense would generally
be limited to kin and the smaller face-to-face groups. In these cases the
willingness to make considerable self-sacrifice would favor one’s descen-
dants and tend to be selected. Turning to the other extreme, a society
which had a strong propensity to supererogatory conduct in its relations
with other societies would jeopardize the existence of its own distinctive
culture and its members would risk domination. Therefore one might
conjecture that the capacity to act from the more universal forms of ra-
tional benevolence is likely to be eliminated, whereas the capacity to fol-
low the principles of justice and natural duty in relations between groups
and individuals other than kin would be favored. We can also see how the
system of the moral feelings might evolve as inclinations supporting the
natural duties and as stabilizing mechanisms for just schemes.
28
If this is
correct, then once again the principles of justice are more securely based.
These remarks are not intended as justifying reasons for the contract
view. The main grounds for the principles of justice have already been
presented. At this point we are simply checking whether the conception
already adopted is a feasible one and not so unstable that some other
choice might be better. We are in the second part of the argument in
which we ask if the acknowledgment previously made should be recon-
sidered (§25). I do not contend then that justice as fairness is the most
stable conception of justice. The understanding required to answer this
question is far beyond the primitive theory I have sketched. The concep-
tion agreed to need only be stable enough.
77. THE BASIS OF EQUALITY
77. The Basis of Equality
I now turn to the basis of equality, the features of human beings in virtue
of which they are to be treated in accordance with the principles of
justice. Our conduct toward animals is not regulated by these principles,
or so it is generally believed. On what grounds then do we distinguish
between mankind and other living things and regard the constraints of
justice as holding only in our relations to human persons? We must exam-
ine what determines the range of application of conceptions of justice.
To clarify our question, we may distinguish three levels where the
concept of equality applies. The first is to the administration of institu-
tions as public systems of rules. In this case equality is essentially justice
28. On this last point, see Trivers, ibid., pp. 47–54.
441
77. The Basis of Equality

---

as regularity. It implies the impartial application and consistent interpre-
tation of rules according to such precepts as to treat similar cases simi-
larly (as defined by statutes and precedents) and the like (§38). Equality
at this level is the least controversial element in the common sense idea of
justice.
29
The second and much more difficult application of equality is to
the substantive structure of institutions. Here the meaning of equality is
specified by the principles of justice which require that equal basic rights
be assigned to all persons. Presumably this excludes animals; they have
some protection certainly but their status is not that of human beings. But
this outcome is still unexplained. We have yet to consider what sorts of
beings are owed the guarantees of justice. This brings us to the third level
at which the question of equality arises.
The natural answer seems to be that it is precisely the moral persons
who are entitled to equal justice. Moral persons are distinguished by two
features: first they are capable of having (and are assumed to have) a
conception of their good (as expressed by a rational plan of life); and
second they are capable of having (and are assumed to acquire) a sense of
justice, a normally effective desire to apply and to act upon the principles
of justice, at least to a certain minimum degree. We use the charac-
terization of the persons in the original position to single out the kind of
beings to whom the principles chosen apply. After all, the parties are
thought of as adopting these criteria to regulate their common institutions
and their conduct toward one another; and the description of their nature
enters into the reasoning by which these principles are selected. Thus
equal justice is owed to those who have the capacity to take part in and to
act in accordance with the public understanding of the initial situation.
One should observe that moral personality is here defined as a potential-
ity that is ordinarily realized in due course. It is this potentiality which
brings the claims of justice into play. I shall return to this point below.
We see, then, that the capacity for moral personality is a sufficient
condition for being entitled to equal justice.
30
Nothing beyond the essen-
tial minimum is required. Whether moral personality is also a necessary
29. See Sidgwick,