cating resources in more conventional, tangible commodities such as fish or chips (of both the computer and the potato varieties).1 This conclusion rests on the fundamental insight that ideas—especially ideas tested and reduced to codified scientific and technological information through R&D activities—have some important attributes found in public goods, goods that are widely available to individuals whether or not they paid for them. Correspondingly, they may be better understood by studying other public goods, such as a smog-free environment or defense against nuclear missile attack.
An idea is a thing of remarkable expansiveness: it can spread rapidly from mind to mind without any reduction in its meaning and significance for those into whose possession it comes. Thomas Jefferson remarked upon this attribute, which permits the same knowledge to be used jointly by many individuals at once: ''He who receives an idea from me, receives instruction himself without lessening mine; as he who lights his taper at mine receives light without darkening me. . . ." Economists have pointed out that the potential value of an idea to any individual buyer generally would not match its value to the social whole. The latter value, however, is not readily expressed in a willingness to pay on the part of all who would gain from the illuminating idea. Once a new bit of knowledge is revealed by its discoverer(s), some benefits will instantly spill over to others who are therefore able to share in its possession. Commodities that have the property of expansibility, permitting them to be used simultaneously for the benefit of a number of agents, are sometimes described as being nonrival in use: although the cost of the first instance of use of new knowledge may be large, in that it includes the cost of its generation, further instances of its use impose at most a negligible incremental cost.2
This formulation ignores the cost of training potential users to be able to use new information. Although it is correct that there can be fixed costs of access to the information, these costs do not invalidate the proposition that reuse of the information will neither deplete it nor impose further costs. It may be costly to teach someone how to read the table of the elements or use differential calculus, but any number of individuals thus instructed can go on using that knowledge without incurring further costs.
The second feature of ideas is that it is difficult, indeed costly, to retain exclusive possession of them while putting them to use. Another disadvantage of exclusivity is that results obtained by methods that are not or cannot be revealed often are felt to be less reliable. Of course, it is possible to keep a piece of information or a new idea secret. Producing results not achievable otherwise, however, indicates the existence of a