In this paper, using new evidence from Pontic Greek (PG) in addition to Standard Modern Greek, we argue that the Person Case Constraint (PCC), generally presumed to be an irreducible morphosyntactic constraint on clitic pronoun combinations and argued by several to provide evidence of feature-driven syntactic operations, is a direct consequence of processing considerations, these new data being inexplicable under any of the current feature-driven analyses , in which syntax is defi ned as the monotonic incremental growth of semantic structure, with structural underspecifi cation and update as the core syntactic notion, we argue that the PCC is wholly due to restrictions on tree-growth imposed by the logic of fi nite trees: that these should underpin observed gaps in possible clitic combinations is due to clitics being calcifi ed refl exes of previously available tree-growth update-sequences whose variability is the source of word order variation. More specifi cally, we argue that PCC eff ects, including the problematic PG data, are the consequence of a tree-logic restriction that only one unfi xed node can be present in a tree at any stage in the tree growth process. PG, a dialect in which no 3rd person clitic clusters are allowed, provides strong evidence for such a feature-free account. Contrary to current feature-based analyses, which would preclude such data, the analysis presented here is shown to directly predict the Pontic Greek data, thus pointing towards a feature-free account of the PCC.