In the Phase Theory of Cyclicity, Chomsky (2000, et seq.) introduced a novel concept of Lexical Subarray (LSA), which determines a phase. Chomsky claims that LSA s "propositional," and hence can be selected straightforwardly from the initial Lexical Array; LSA is determined by a single choice of C or of v.
In this paper, I show that the determination of LSA is not so straightforward that operative complexity can be reduced as Chomsky envisages. It entails combinatorial explosion of an exponential order. The question, which motivated the concept of LSA, why Merge of an expletive does not always preempt Move, can be answered by a dynamic economy principle of derivation I propose, Minimum Feature Retention (MFR) that dynamically makes a locally deterministic choice, without a predetermined preference for one operation over another, between (external) Merge and Move (internal Merge). MFR involves one-step "look-ahead," which is crucial for the notion of "derivational locality." In addition, I propose that the expletive there is selected as a kind of "External Argument" of v, which dissolves an apparent problem for MFR.