What is natural capital? What is natural capital depreciation and how can it be incorporated into national income accounting? What is the principle of natural capital sustainability? What is throughput? What is the difference between a closed and open system? Why is the issue of scale important in ecological economics? What do we mean by "empty-world" and "full-world" economics? What is the difference between weak and strong sustainability? Why is ecological complexity important to ecological economists? What is the precautionary principle?