Grammaticalization

Step 2 of interlanguage development:

learning grammatical words and assembling words into meaningful phrases and sentences.

At this stage, learners begin to add more grammar and structure to their interlanguage. Modal auxiliaries and Circumstantials help the learner to express him- or herself more clearly. The learner's lexicon also continues to develop and allows for more precise and varied communication.

Bruntt, Karen and Bryanne, Ulla. Handbook for Grammar Detectives, page 25-26.