Trained within the Neo-Kantian Marburg School, he initially followed his mentor Hermann Cohen in attempting to supply an idealistic philosophy of science.

Though his work received a mixed reception shortly after his death, more recent scholarship has remarked upon Cassirer's role as a strident defender of the moral idealism of the Enlightenment era and the cause of liberal democracy at a time when the rise of fascism had made such advocacy unfashionable.

He then did his doctoral work at University of Marburg where he studied Philosophy under Hermann Cohen and Paul Natorp and Mathematics under Friedrich Schottky.

[5] In 1899 he graduated with a dissertation on René Descartes's analysis of mathematical and natural scientific knowledge entitled Descartes' Kritik der mathematischen und naturwissenschaftlichen Erkenntnis [Descartes' Critique of Mathematical and Scientific Knowledge]) and completed his habilitation in 1906 at the University of Berlin with the dissertation Das Erkenntnisproblem in der Philosophie und Wissenschaft der neueren Zeit: Erster Band [The Problem of Knowledge in Philosophy and Science in the Modern Age: Volume I]).

Donald Phillip Verene, who published some of Cassirer's papers kept at Yale University, gave this overview of his ideas: "Cassirer as a thinker became an embodiment of Kantian principles, but also of much more, of an overall movement of spirit stretching from the Renaissance to the Enlightenment, and on to Herder's conception of history, Goethe's poetry, Wilhelm von Humboldt's study of the Kavi language, Schelling's Philosophie der Mythologie, Hegel's Phenomenology of Spirit, and Vischer's conception of the aesthetic symbol, among many others.

His reading of the Scientific Revolution, in books such as The Individual and the Cosmos in Renaissance Philosophy (1927), as a "Platonic" application of mathematics to nature, influenced historians such as E. A. Burtt, E. J. Dijksterhuis, and Alexandre Koyré.

Mazlish (2000)[citation needed], however, notes that Cassirer in his The Philosophy of the Enlightenment (1932) focuses exclusively on ideas, ignoring the political and social context in which they were produced.

Cassirer's last work, The Myth of the State (1946), was published posthumously; at one level it is an attempt to understand the intellectual origins of Nazi Germany.

Cassirer claimed that in 20th-century politics there was a return, with the passive acquiescence of Martin Heidegger, to the irrationality of myth, and in particular to a belief that there is such a thing as destiny.