This chapter suggests that one relevant source for checking hypotheses about the content of the law is judgments that deal with similar issues. Reasoning by analogy can be used to discover law conditioned on the existence of policy reasons that justify the analogy from one doctrine to another. The problem is that sometimes the policy outcomes underlying different doctrines are not clearly observable. Several techniques have been developed in the literature to reach the conclusion that different doctrines have the same policy outcomes even when the policy outcomes themselves remain unknown. By presenting these techniques, the chapter explains how hypotheses about the state of the law can be checked against judgments on similar issues.