Horkheimer and Pollock leveraged emigration threats to win study rights from their fathers.

Evidence

Adolph Lowe, a childhood friend from Stuttgart, remembers Horkheimer and Pollock giving their fathers an ultimatum when they were in England: either they were to be allowed to return to Germany to begin their studies or they would emigrate. The senior Horkheimer and senior Pollock seem to have given in without much resistance (conversation with Lowe, New York, N.Y., December 28, 1971). — Martin Jay, The Dialectical Imagination, 988