Interlanguage and the pro-drop parameter

There is a relatively stable period in child L 1 acquisition during which surface subjects can be omitted. This period is also characterized by the absence of modals and expletives. With the emergence of modals and expletives, absent subjects disappear. This sequence has been attributed to the constraints of Universal Grammar (UG), a parameterized system with various settings depending on the language. The same sequence has also been observed in the interlanguage of a Spanish speaker learning English, suggesting that UG might also constrain interlanguages, and that a major part of L2 learning may be resetting the values of UG parameters.