Auctioning permits has significant economic advantages over grandfathering. Another important aspect of transferable permits is whether they are auctioned or allocated via grandfathering. A question has been raised over the grandfathering of allowances. In Coase's model of social costs, either choice (grandfathering or auctioning) leads to efficiency. The grandfathering method for calculating national emissions budgets uses this principle. Any modification to the existing structure would result in the loss of the grandfathering. There will be no "grandfathering in" of past content.