The document discusses individual differences in language aptitude. It defines aptitude as a learner's capacity for learning a task based on their enduring characteristics. Language aptitude refers to cognitive differences between learners and their ability to learn a language. Between 1920-1930, researchers developed early language aptitude tests to predict learners' performance. These tests used analytical and synthetic approaches. Modern tests like the MLAT and PLAB further researched aptitude and its components like memory, auditory ability, and linguistic ability. The document discusses ongoing issues around what aptitude measures, its relationship to age, intelligence, teaching methods, and the purpose of aptitude testing.