So long as the environment is seen to be a set of resources and assets that feed the economic system and economic growth has priority, then it makes sense to believe that substitutes can be found when some of these resources and assets run out or are damaged. Vandana Shiva argues that the fallacy of "the non-destructibility of capital and the substitutability of capital and nature" preserves the sanctity of economic growth:
since industrial raw materials and market commodities have substitutes, sustainability is translated into substitutability of materials, which is further translated into convertibility into profits and cash.
This notion of substitutability is inherent in the idea of `valuing' the environment and also economic instruments. The way that environmental concerns are to be integrated into economic decisions is by estimating the monetary value of the environmental damage that an activity might do and weighing such costs against the benefits of going ahead anyway. This assumes that the financial and other gains from a project can make up for these environmental losses, that they are in some way substitutable for one another.
Likewise the argument for incorporating monetary estimates of environmental loss in measures of GNP also assumes that "natural capital" and "human capital" are interchangeable. The implicit premise is that such a modified GNP measure will then reflect increasing welfare as long as the total capital, natural plus human, increases. Accepting a GNP figure modified in this way means accepting that loss of nature can be made up for by corresponding increases in wealth.
Finally, economic instruments give individuals and firms the choice of paying charges or preventing pollution as if one were substitutable for the other. The purpose of pollution charges, for example, is to internalise environmental costs so that they become part of a firm's profit calculations like the costs of labour, materials and services that they obtain on the market. The firm can then choose to reduce those environmental costs by reducing their pollution. On the other hand the firm may chose to reduce other costs instead, for example labour costs.
The purpose of giving environmental `resources' a price is so that they will be valued in the same way that other resources that are on the market are valued. Some environmentalists may be reassured that this means more account will be taken of the environment. On the other hand, this can be seen as a devaluation of the environment because it brings it down to the same level as other commodities that can be bought and sold. Its value is reduced to an economic value and it is then treated as a substitutable part of the economic system.