Far from being idiosyncratic or cyclical, the development of the Latin verb is characterized by a two-pronged evolution. The recently created auxiliary habeo "to have" has replaced sum "to be" as a temporal auxiliary. This substitution reflects the change from an aspect — to a tense — dominated verbal system. Moreover, the sequences verb + auxiliary element have been reversed: in contrast to Latin, the French morphological marker precedes the lexeme. This change is consistent with the evolution of syntactic and morphological structures from left- to right branching. Therefore, the development of the Romance verb is part of the unidirectional switch (1) from left- to right-branching structures and (2) from an aspect — based to a tense — based verb system. This two-pronged evolution characterizes the history of other Indo-European languages.