This paper highlights two recurring facets of the way UK courts approach the construction of patent claims: the adoption of methods typically applied to the interpretation of contracts and the recognition that immaterial variations not expressly claimed nevertheless fall within the scope of protection. Drawing on the normative implications arising out of Ronald Coase's paper on the problem of social cost, this paper argues that the patent system operates as a substitute for an explicit bargain between economically active entities operating in the market under which a duty is accepted by one party in return for acceptance of a burden of risk by the other. This perspective incorporates both the static costs and the dynamic benefits of the system and accords with the monopoly-profit-incentive theory most commonly advanced in support of the patent system. It is shown how the contemporary approach to claims construction is supported by the object of giving effect to the presumed intentions of the parties to this hypothetical bargain and that this underpins both the implication of terms which go beyond those expressly agreed to by parties to a contract and the construction of patent claims so as to embrace immaterial variations not expressly within their scope.