the actual basis of all symbolic forms

"In the winter of 1919, as he passed through the machine-gun fire of the Spartacist uprising, this time on his way to the university rather than the press office, he was already working on the manuscript of the first volume, concerning the phenomenon of human language as the actual basis of all symbolic forms. Cassirer was sure that he was working on something of consequence, the great idea of his life. And, as if summoned by fate, in May 1919—around the time that the corpse of Rosa Luxembourg, murdered in January, was fished out of the Landwehr Canal—he received a letter from the newly established Hamburg University."
~~ from Time of the Magicians: Wittgenstein, Benjamin, Cassirer, Heidegger, and the Decade That  Reinvented Philosophy by Wolfram Eilenberger