The December 1951 version of Morphophonemics of Modern Hebrew that has been available to scholars since its publication in 1979 is very different from the original M.A. thesis accepted six months earlier. To assess the importance of this work to the history of linguistics, a number of factors must be studied: Chomsky’s background in Semitic philology and linguistics; the other influences to which he was exposed to date; the degree to which those influences were assimilated and/ or transcended; the archival nature of the materials concerned and those that followed; and the nature and causes of the differences between the versions.