This book concentrates on the way young children's speech may vary between the pronouns I, my, and me as the subject of a sentence. For example, one child in the study at 30 months of age alternated between my and I as the subject form, as seen in these two utterances (p. 73):

(1) I like Anna,

(2) My like vanilla.

The fundamental claim is that such variation is motivated and principled. The author writes:

One might want to claim instead that the children were simply confused about the distinctions between various self-reference forms and thus might use them in free variation. (p. 58)

No one has ever claimed that children were “simply confused” when they made pronoun Case errors, and this book's lack of attention to opposing explanations for pronoun Case errors is a major flaw. For those interested in learning more about the phenomenon some important citations are Chiat (1981), Loeb and Leonard (1991), Powers (1995), Rispoli (1994), Schutze and Wexler (1996), and Vainikka (1994). Loeb and Leonard (1991), Powers (1995), and Schutze and Wexler (1996) hold that the child's inability to accurately assign Case leads to these errors as well as a host of simultaneously occurring phenomena such as inaccurate production of agreement and tense marking. Rispoli (1994) views these errors as the result of paradigm building.