Statement I: Strong sustainability is an approach that requires maintaining the stock of natural capital. It assumes that natural capital and human- made capital are largely complements and not easily substitutable. It emphasizes preserving critical natural assets individually. Statement II: Weak sustainability assumes that natural capital and human-made capital are substitutes. It focuses on maintaining the total value of the aggregate capital stock (sum of natural and human-made capital). It implies that a decline in natural capital is acceptable as long as it is compensated by an increase in human-made capital, thereby maintaining the overall value.