It has been stated that nurse education in the United Kingdom (UK) currently draws upon Schön's concept of the reflective practitioner, and Benner's concept of the expert. Studies have explored the claim that experienced expert practitioners are unable to articulate all they know, and that their theoretical knowledge and clinical skills are of a qualitatively different type from that of novice practitioners. This paper aims to explain the differences between expert and novice performance using the example of administering an intramuscular injection of an analgesic agent to a patient in pain. Theoretical concepts concerning the nature of expertise are used to evaluate novice/expert performance in nursing. Criticisms of Benner's theory are developed in relationship to her methodology and the interpretation and assessment of nursing practice.