In a finite world due to be sucked into the sun in only 7.5billion years, nothing is truly sustainable. "Sustainable" has become so meaningless that the local chamber of commerce referred to a "return to a sustainable economy" recently, so would we be lost for words if we banned the use of "Sustainable"?
I'm going to try very hard to remove the word from my vocabulary from now on and use some of these instead:
Resilience - the ability to bounce back, and often the opposite of efficiency. A highly efficient system is designed for the highest gain in the short term. It is tuned to current circumstances and as soon as those circumstances change it is no longer efficient. The more efficient and specialised a system, business or organism becomes the less adaptable and resilient. Resillience is about the boring stuff. The boring banks were more resillient, the boring businesses producing essential goods and services for local markets - funeral directors, tyre sales, food markets are all ticking away. Resillience is about reliability and repairability. Resillience is about having an infrastructure we can trust - energy, transport, broadband, water.
Continuity - the value in keeping some things the same while others change. The loss of a business is not simply a monetary loss for the economy but the loss of intelligence. An established company has an intelligence and learning of it's own which is held by it's staff. While some of that intelligence may be written down, breaking up the people means losing that intelligence. Continuity is about keeping and using that collective intelligence, even if the original purpose has changed.
Balanced Portfolio - In the old days, a couple of decades ago, financial advisors talked about a balanced portfolio. You had your safe (!) bonds and blue chip stocks, your more risky stocks and shares and a few high risk investments. If our economy was a balanced portfolio, the safe investments would be investing in our own elf-sufficiency, making goods and services that are needed in our own economy. The medium risk would be making goods for export markets, attracting multinational FDR and investing in foreign businesses. High risk would be relying on cycles that are likely to be short lived - housing booms have historically been followed by housing busts and there seems to escape from that cycle.
Natural Lifespan - while long term thinking, continuity and resilience have their place, being able to exploit short term opportunities, the high risk element of the balanced portfolio, is also of great benefit and the trick here is to build in the demise as well as the creation and the skill is in knowing when to change.
What all of these words have in common is a longer term view of success than we have become used to, so rather than asking for the speaker's or author's definition of "Sustainable" as I have in the past, I will ask "Do you mean continue indefinitely, or do you have a more realistic timeframe in mind?".