Dreben was both an expert logician, and careful historian of ideas and interpreter of historical texts. In the 1950s, he found a copy of Jacques Herbrand's Ph.D. thesis, submitted to the University of Paris in 1929 and thought lost. (Herbrand died in 1931 before either marrying or starting his career.) Dreben found a number of significant errors in the thesis, as well as evidence of haste and carelessness in its preparation. In particular, in Herbrand's proof, a crucial lemma was fatally flawed, but Dreben found another way of proving the essential conclusions of the thesis. Dreben's introduction to the translation of Herbrand's thesis in includes a concise description of his work on Herbrand's writings.