orientation of technological development, and in- stitutional change are all in harmony and enhance
both current and future potential to meet human needs and aspirations’ WCED, 1987: 46.
This definition involves an important transfor- mation and extension of the ecologically-based
concept of physical sustainability to the social and economic context of development Adams, 1990.
Thus, terms of sustainability cannot exclusively be defined from an environmental point of view, or
on the basis of attitudes. Rather, the challenge is to define operational and consistent terms of sus-
tainability from an integrated social, ecological, and economic system perspective. This gives rise
to two fundamental issues that need to be clearly distinguished before integrating normative and
positive issues in an overall framework.
The first issue is concerned with the objectives of sustainable development; that is, ‘what should
be sustained’ and ‘what kind of development do we prefer’. These are normative questions that
involve value judgments about society’s objectives with respect to social, economic, and ecological
system goals cf. Barbier, 1987; Munasinghe, 1993; Khan, 1995. These value judgments are
usefully expressed in terms of a social welfare function which allows an evaluation of trade-offs
among the different system goals.
The second issue deals with the positive aspect of sustainable development; that is, the feasibility
problem of ‘what can be sustained’ and ‘what kind of system we can get’. It requires one to
understand how the different systems interact and evolve, and how they could be managed. For-
mally, this can be represented in a dynamic model by a set of differential equations and additional
constraints. The entire set of feasible combina- tions of social, economic and ecological states
describes the intertemporal transformation space of the economy in the broadest sense.
To date, various definitions and stationary-state criteria of sustainability have been proposed.
Many writers have been concerned with partial questions, such as technological assumptions and
the substitutability of natural resources in eco- nomic transformation processes, and the resilience
and criticality of ecological processes cf. Pearce et al., 1994; Turner et al., 1994; Atkinson et al.,
1997. But, the social dimension did not receive the same attention, and has not adequately been
integrated into formal analysis. Moreover, posi- tive aspects of feasibility and the normative con-
tent of sustainable development have not been clearly distinguished.
Given these circumstances, the aim of this pa- per is to elaborate a social value function which is
compatible with the general objective and system requirements of sustainable development. In the
next section, I briefly review some fundamental principles of sustainability from an ecological-eco-
nomic perspective. In Section 3, I present an extension of these principles to the social context,
and provide a formal approach which includes distributional concerns and population growth. In
Section 4, I address principles of basic human needs, and criticality of ecological and social cap-
ital. Building on this background, I formulate a ‘sustainability-based social value function’, which
integrates individual preferences and system re- quirements of sustainable development. Conclud-
ing remarks about the use of this new value function and the feasibility of sustainable develop-
ment follow in Section 5.
2. Ecological and economic interpretations of sustainability
Divergent interpretations and opposing defini- tions of sustainability are sources of confusion,
rather than contributions that could help to rein- force the root idea of sustainable development. As
a consequence, there is disagreement about the conceptual and operational content of ‘sustain-
ability’. This has resulted in different paradigms that are referred to as ‘weak’ and ‘strong’ sustain-
ability principles, respectively cf. Turner et al., 1994; Hediger, 1999.
In general, ‘weak sustainability’ is defined as an economic value principle which is founded within
the body of neoclassical capital theory. It requires that some suitably defined value of aggregate
capital — including human-made capital and the initial endowment of natural resources and social
assets — must be maintained intact over time. However, this principle remains unclear. The ob-
jective of weak sustainability can be variously defined. In narrow terms, 6ery weak sustainability
‘Solow sustainability’ requires that the general- ized production capacity of an economy is main-
tained
intact, such
as to
enable constant
consumption per capita through time Solow, 1986. In broader terms, weak sustainability re-
quires that the welfare potential of the overall capital base remains intact Pearce et al., 1994.
The latter principle allows the integration of dif- ferent objectives of development, whereas the for-
mer is restricted to consumption per capita.
In contrast, the idea of ‘strong sustainability’ emerged from the pre-analytic vision of ecological
economics that the economy is an open subsystem of the finite and non-growing global ecosystem
Costanza et al., 1991; Daly, 1991. This bio-phys- ical principle is founded upon the laws of thermo-
dynamics, and requires that certain properties of the environment must be sustained. Yet, this has
been variously interpreted in the literature.
In the most restricitive version, 6ery strong sus- tainability calls for a set of stationary-state con-
straints that must be imposed on the scale of the macro-economy Costanza, 1991; Daly, 1991.
Less restrictive, strong sustainability is defined as an ecosystem principle, which better corresponds
to the concept of sustainable development. As advocated by the WCED 1987: 46, ‘sustainable
development requires that the adverse impacts on the quality of air, water, and other natural ele-
ments are minimized so as to sustain the ecosys- tem’s overall integrity.’ This imperative can either
be translated in a principle of maintaining the ecological capital intact over time Hediger, 1998,
or restricting environmental degradation above some critical level of resilience beyond which the
ecosystem could not recover from shocks or stress Common and Perrings, 1992; Pearce et al., 1994;
Perrings, 1996.
In any case, strong sustainability cannot be defined in terms of maintaining the entire natural
resource base natural capital constant over time. Rather, it must be expressed in terms of ecological
capital the ecosystem’s resource base. This view is founded on a distinction between economic
capital, natural capital, and ecological capital Hediger, 1999:
1. Economic capital is defined as an economy’s generalized productive capacity; that is, the
potential to generate income. It consists of manufactured capital machines and build-
ings, immaterial assets knowledge and know- how, social organization, institutions, and the
state of technology, and natural resources including non-renewable resources, renewable
resources, and land that are harvested or de- veloped for use in economic transformation
processes. Correspondingly, economic capital does not include ecological assets that are not
directly used, but that are essential for the functioning of the ecosystem.
2. Ecological capital ecosystem capital consists of the total of renewable resource stocks both
used and non-used in economic production, semi-natural and natural land areas, as well as
ecological factors, such as nutrient cycles, cli- matic conditions, and the resilience of ecosys-
tems. This is the part of natural capital which determines
the overall
quality of
the ecosystem.
3. Natural capital is defined as the natural re- source base of a geographic area. It consists of
the ecological capital and stocks of non-renew- able resources.
4. Total capital is an aggregate of overlapping compartments of economic and natural capital
— that is, the aggregate value of human-made capital, non-renewable resources, ecological
capital — as well as immaterial assets of social capital cf. Section 3.
The relationship between the different compart- ments of capital and the above-mentioned princi-
ples of sustainability can be summarized as follows:
very weak sustainability is defined with respect to economic capital,
strong sustainability is defined with respect to ecological capital, and
weak sustainability is defined with respect to total capital.
Apart from defining an economy’s capital base, sustainable development analysis requires that de-
velopment and conservation goals are made ex- plicit. For very weak sustainability the objective is
to maintain income per capita constant over time. Referring to Hicks 1939, income is defined as the
maximum amount of consumption that can be spent on consumption in one period without reducing real
consumption opportunities in future periods. This is sustainable by definition Daly, 1991. By con-
trast, the objective of strong sustainability is to maintain the ecological capital at the initial level.
This implies an astronomical value given to the environment in comparison with consumption. In
other words, in a strong sustainability framework, the environment can be said to be considered as
sacred capital Taylor, 1996. Finally, the objective of weak sustainability is to maintain the level of
social welfare. With respect to economic develop- ment and the environment, this is the total value
of instantaneous consumption and the environment in an area. Apparently, among the above concepts,
weak sustainability provides the most comprehen- sive approach to sustainable development. It allows
for trade-offs between consumption and environ- mental quality. Moreover, it integrates very weak
and strong sustainability as a special case. However, weak sustainability is not sufficient for sustainable
development, since the latter cannot exclusively be defined with reference to economic development and
the environment.
3. Extension to the social context
