With such a principle of learning, Marx was proficient in English, French, Italian, Spanish, and also learned Russian

In order to complete the article written for the Tribune in time, Marx worked all night, which has become an increasingly regular phenomenon. In the fifties, When Liebknecht was a daily guest at Marx's house, he recalled Marx and said with astonishment:

"He worked for a long time, and, because he was often disturbed during the day (especially in the early days of exile), he stayed up late. It's not too early for us to go home at night. He usually sat down and worked for a few hours, and those hours went on a little longer, almost all night, until he went to bed in the morning. His wife rebuked him harshly on occasion, but he laughed and said that his temper was like this. ”

However, years of hard work like this, no matter how good the quality, can not stand it. From the mid-fifties onwards, Marx suffered from a very painful chronic disease, and his condition was getting worse and worse, which was the result of long poverty and exhaustion.

Marx was extremely serious and rigorous in his scientific work. He followed the principle that "the study must possess the material in detail, analyze its different forms of development, and explore the internal relations of these forms." Only after such work has been done can the actual movement be properly described. ”

In order to compile and study the materials he collected, Marx was not afraid to do many time-consuming trivial things without fear. He carefully checked every piece of evidence in the book. He always looked for the original material, indirectly according to which he did not adopt. Even for unimportant arguments, he had to compare the original materials, so that he made a special trip to the library for this purpose.

In order to be able to read first-hand material, he learned again within a few years — he was already fluent in French and English, Italian and Spanish, and finally, at the age of fifty, Russian. He always liked to say, "Foreign Chinese is a weapon in the struggle of life."

Every time he wrote a book, he always accumulated a lot of information, such as notes, synopsis, tables, outlines, and practical plans, and compiled a detailed table of contents and a synopsis of each content. He often wrote his insights and research results on 2 drafts of the larger folio. This is for your own review only, and it is not yet finalized. Only after these steps did he begin meticulous processing for publication.

He first read a large number of books, newspapers, professional magazines, official gazettes, parliamentary records and all available economic and social statistical materials, industrial, commercial and exchange tables, etc., and studied and made full use of these materials over the years.

(Gemkov's "Marx" reading notes)