The Difference Between the Democritean and Epicurean Philosophy of Nature (German: Differenz der demokritischen und epikureischen Naturphilosophie) is a book written by the German philosopher Karl Marx as his university thesis. Completed in 1841, it was on the basis of this work that he earned his Ph.D.[1] The thesis is a comparative study on atomism of Democritus and Epicurus on contingency.