Work on coordination has been concerned with the conditions in which elements can be “shared” between two conjuncts since at least Ross (1967). This paper aims to describe a curious case of apparently obligatory sharing, where coordinated clauses below a shared element in C – i.e. coordinated TP clauses – are required to “share” a single initial subject unless the subject of the second clause is focused.
I argue that this restriction arises from properties of cyclic linearization (Fox and Pesetsky 2005, Richards 2010). Limitations of the linearization algorithm prevent it from distinguishing DP arguments from one another (Richards 2010). What distinguishes the subjects of TPs from arguments of other clausal conjuncts is that they are both visible to the linearization algorithm on a single cycle of Spell Out. Unable to distinguish the two subjects, this algorithm linearizes them in a single position, except in cases where subject-oriented focus requires an overt subject in the second clause. The final section of the paper extend the analysis to SLF coordination (Höhle, 1983, 1990), which shows a similar restriction on overt subjects in the second conjunct.