What is sustainability?

"Sustainability," like "sustainable development," is a notoriously vague, malleable concept. Countless scholars, pundits, activists, and more have tried to define sustainability in order to give it meaning and protect it from the careless or malicious use of greenwashers. To me, sustainability has a few key qualities:

• it's long-term. Decisions are made based on positive outcomes decades or centuries in the future, not just tomorrow. Although building pollution scrubbers on coal-fired power plants may cost money upfront, the long-term health effects make them a valuable investment.
  
• it acknowledges natural limits. The goal is not growth, but sufficiency, and understanding limits to natural systems, such as "sustainable yields" of timber, fish, and wheat.
  
• it's system-based. Solutions improve system health and viability by considering corollary effects of decisions. Smart growth development promotes health, lowers transportation and infrastructure costs, improves the local economy, and builds a sense of place: building the right systems leads to far-reaching positive effects.
  
• it's equitable. A long-term viewpoint implicitly promotes intergenerational equity. So it's important to consider intragenerational equity as well.
• it's democratic, often even consensus-based. Democratic, consensus-building decision-making processes reinforce the personal change and long-term system stability necessary for sustainability to function.
• it's not just about the environment. Because sustainability works with entire systems, it requires economic, social, and institutional viability as well as environmental quality.