Sustainability in these programs is generally defined to include economic, environmental, and social sustainability, collectively known as the Triple Bottom Line. For each of these domains, sustainability means that it will be possible to continue through the foreseeable future, at least, without major breakdowns, such as
- Economic: running out of oil or other natural resources and having nothing to replace them on the scale required
- Environmental: loss of habitat, species, and whole ecologies; global warming
- Social: overpopulation beyond the carrying capacity of the earth; consequences of eliminating poverty within the current economic model
- Externalities: economically significant effects of manufacturing and trade on those who are not part of the industry or market in question. The classic example of a negative externality is pollution, while the largest current issue is global warming. The literature has identified many others, and many positive externalities, and has proposed many controversial measures to improve the balance.
- Natural resources: conventional accounting, including national accounts, treats extraction of finite natural resources as income, priced at the cost of extraction, and not as depletion of non-renewable natural capital. The resources of nature come to us for free. They are of infinite value from the point of view of preserving and sustaining life, but may not be subject to trading in a market, as in the case of air for breathing, for agriculture, or for burning fuels.
- The problem of value: conventional economics can describe the process of setting prices in a marketplace through the interaction of supply and demand, but cannot adequately explain value. (Though not for lack of trying. See Labor Theory of Value and Util for examples.) The most economists generally agree on is that an individual purchaser in a free market will only buy something worth more to that individual than the price, and that the seller values the goods less than the price, so that both sides come out ahead.
- Participation: The free market is not free to those who have no access to it.