Roger Brow and his team study of the language development of three children (Adam, Eve and Sarah) they found that fourteen grammatical morphemes which are obligatory in English. That shows some of morphemes they studied such as present progressive (-ing), plural (-s), possessive (‘s). Besides, he and his team found that a child who had mastered the grammatical morphemes at the list was sure to have mastered those at the top, but the reverse was not true. So, there was evidence for a developmental sequence or order of acquisition. However, the children did not acquire the morphemes at the same age or rate. Eve had mastered nearly all the morphemes before she was two and a half years old, while Sarah and Adam were still working on them when were three and a half or four years old.