Many of Meehl's interests converged in his work on personality assessment. In empirical research, development of the K scale of the Minnesota Multiphasic Personality Inventory and various scales of other tests are noteworthy, but his most profound contributions were conceptual and philosophical. Essays on the role of base rates in clinical decision and on construct validity in psychological tests provided vital insights on core issues in assessment. The concept of nomological nets allowed systematic investigation of unobservable theoretical entities, with liberating effects on all natural sciences. An active clinician, Meehl understood deeply the complexities of professional service, but his insistence on empirical validation as the ultimate arbiter of the value of any procedure required all attainable rigor in the scientific foundations of clinical practice.