As far as learning was concerned, Marx was, and still is incomparably more advanced than I. I knew nothing at that time of political economy, I had not yet rid myself of my metaphysical aberrations, and my socialism was only instinctive. Although younger than I, he was already an atheist, a conscious materialist, and an informed socialist. It was precisely at this time that he was elaborating the foundations of his system as it stands today. We saw each other often. I greatly respected him for his learning and for his passionate devotion- thought it was always mingled with vanity- to the cause of the proletariat. I eagerly sought his conversation, which was always instructive and witty when it was not inspired by petty hate, which alas! was... (From : Marxists.org.)