Internal processes include the context of the utterance, the state of mind of the speaker, his life's experience - the realm of the unpredictable. The concept of situation is inoperable if we extend the notion to include internal processes. Language users are real people - not just robots in situations. Language teaching is then organised in terms of content rather than form. It will produce communicative competence in the learners and motivation will be sustained.
Needs are difficult to define.
The opportunity to actually use language is often deferred. Situational analysis predicts lexical need. The individual is the master of what he chooses to say, but has no comparative control of what he hears. Less successful course books of the late 1970s and early 1980s by other writers, who were good at espousing the theory, included Communicate Cambridge 1979 and Approaches Cambridge 1979.