Although the view that, once discovered, ideas can be imitated for free by anybody is pervasive, it is far from the truth. While it may occasionally be the case that an idea is acquired at no cost—ideas are generally difficult to communicate, and the resources for doing so are limited. It is rather ironic that a group of economists, who are also college professors and earn a substantial living teaching old ideas because their transmission is neither simple nor cheap, would argue otherwise in their scientific work. Most of the times imitation requires effort and, what is more important, imitation requires purchasing either some products or some teaching services from the original innovator, meaning that most spillovers are priced.
