This document discusses the difference between linguistic competence and performance. Competence refers to a person's underlying knowledge of language rules, while performance is how that knowledge is applied in real-time speech and writing. Competence involves knowledge of morphology, syntax, semantics and pragmatics, while performance can be impacted by psychological factors like memory limitations or fatigue. Mistakes in performance do not necessarily mean a lack of competence if the speaker recognizes the mistakes. The relationship between competence and performance illustrates that knowing a language's rules differs from real-world application of that knowledge.