Contracts are risk allocation mechanisms and, as with legal relationships generally, are social relationships. If circumstances change, the content of such relationships also changes. Adjusting such relationships to changed circumstances may be done either using a bottom-up approach, via courts, or in an top-to-bottom approach by the legislator. Implied terms, frustration of purpose, impossibility, judicial amendment of contract and the adaptive application of the rules concerning breach of contract are the tools of judicial adaptation. Intervention via legislation may be more efficient if there are a large number of cases. While legislative or administrative rule-making is determined by political decisions, judge-made rules are influenced by the constrained options of judges. That is, the latter cannot impose a standard of conduct on non-litigants, and the courts cannot handle all legal problems—many of which are not brought to court or end in settlement.