The text suggests that substitutability can affect demand for public goods and bads in the same way that it does for private goods and bads. To be more concrete, consider trying to estimate damages from an oil spill that caused the closure of several beaches along a coastal area. Why is it important to consider whether other local beaches were left uncontaminated and therefore did not close?

Individuals may also have the opportunity to substitute across time as well as space in their consumption of environmental goods. What do we mean by substitution across time and why is it important in estimating the damage in a case such as this one?