Breton tensed verbs show a synthetic/analytic alternation (I.know vs. to.know I.do), that is not conditioned by their semantic or aspectual structure but by their syntactic environment, namely word order. Such a paradigm of verb-doubling poses a strong case against iconicity, because knowing where a verb can double requires full information about the entire derivation of the sentence. The sentence is correct if and only if the tensed element is not at the left edge of the sentence. The infinitive form of the analytic construction prevents the tensed element from occurring in the most left-edge position. This paper proposes that the analytic structure (to.know I.do) responds to the same trigger as expletive insertion (expl I.know). I claim that analytic tense formation is a last resort strategy that forms the equivalent of an expletive by excorporation of the verbal root out of the tensed complex head. The excorporated lexical verb appears fronted as an infinitive form by default. The tensed auxiliary is either realized as a dummy 'do' auxiliary (to.know I.do), or, for an idiosyncratic list of verbs, as the tensed reiteration of the excorporated verb itself (do.ubling; to.know I.know).< Leer menos