Dialectic

Marx and Engels wrote in many books that the opposites of their ''materialism'' and ''dialectics'' were ''idealism'' and ''metaphysics''.
In other words, rather than talking about it in your head, it is important to scientifically confirm its long history and view it as something that is constantly changing, like cells, the earth, and the universe.

And most importantly, when Marx and Engels saw workers in Manchester, England suffering from long working hours due to the tyranny of capitalists, they could not leave them alone and created a huge theory to save them.
This action in reality is what makes them so different from other philosophers and thinkers.

For this purpose, Marx went to the library every day and made extensive transcriptions on the backs of poor quality paper (he was poor).
From classical philosophy to economics (just as Engels said, everything in this world is connected), He thoroughly researched all genres of scholarship. And he thought by connecting these many categories into one.

As a result, he discovered weaknesses in modern philosophers and thinkers such as Hegel.
And He discovered that modern society is divided into classes.
The word "capitalism", which is now used by capitalists and those in power, was coined by Marx.

“Nature and history all around us interact and intertwine.” (Engels, “New edition: Anti-Dühring: 1” 2001, Shin Nippon Publishing)

Film theory diagram by Eisenstein. At the bottom it says ''dialectics''. (Eisenstein, “Eisenstein Complete Works 6” 1980, Kinema Junposha)