1. Early 1990s, 1940s & 1950s
   1. School of thought
      1. Structural Linguistics
      2. Behavioural Psychology
   2. Themes
      1. Description
      2. Observation performance
      3. Scientific Method
      4. Empiricism
      5. Surface Structure
      6. Conditioning
      7. Reinforcement
2. 1960s, 1970s & 1980s
   1. School of thought
      1. Generative Linguistics
      2. Cognitive Psychology
   2. Themes
      1. Generative Linguistics
      2. Acquisition
      3. innateness
      4. interlanguage
      5. systematicity
      6. Universal Grammar
      7. Competence
      8. Deep Structure
3. 1980s, 1990s, & 2000s
   1. School of thought
      1. Constructivism
   2. Themes
      1. Interactive Discourse
      2. Sociocultural variables
      3. Discovery learning
      4. Construction of meaning
      5. Interlanguage variability
4. Table SLA