Marxist Theory

Marxism, as taught and practiced in the USSR, claims that human society consists of

• base: economic structure (ownership of means of production, relationships between the owners and workers, technology envolved &c)
• superstructure: "culture" (politics, laws, rituals &c)

and the base determines the nature of the superstructure.

Accordingly, the superstructure reflects the class structure of the society. Every law corresponds to the views and protects the interests of the ruling class.

Corollary: Positive vs. Normative

The bourgeois society is run by an oppressive retrograde class of exploiters who make arbitrary legislation without regard for objective laws.

The socialist society is managed by the Communist Party representing workers, the most progressive class, and is armed with the progressive Marxist Theory, which provides an objective scientific basis for legislation.

Practice

Here is how a Soviet/Marxist sociologist would explain some existing laws and customs:

• The Second Amendment to the United States Constitution of the US constitution reflects the interests of the exploiters, who want to own weapons to protect themselves from the people they oppress, while the many US gun control laws reflect the interests of the exploiters, who want guns out of hands of the people they oppress.

• The Soviet culture "Тащи с завода каждый гвоздь - ты здесь хозяин, а не гость" (grab every nail from the plant [you work at] - you are the owner, not a guest here) reflects the base fact of workers' ownership of the means of production, while the anti-theft laws (such as the infamous Law of Three Spikelets) reflect the workers as the owners of the means of production protecting their property from Lumpens.

This is only slightly tongue-in-cheek.

Conclusion

If this sounds like religious drivel, well, it is.

See also my answer to Why did Stalin deem Quantum Mechanics 'counter-revolutionary'?:

Remember that a quote from Marx/Engels/Lenin was enough to win any argument in the Soviet Union.

Quote From the Article

"the USSR accepted certain aspects of international law, and at various times even used general international law to defend its own specific interests, the conceptual framework for such usage being the duality of systems and the class basis of law."

This is just plain opportunism: whenever the international law favored USSR, it said

See, even the corrupt bourgeois law recognizes that we are right!

and when the law disagreed with USSR, it said

we are not bound by the corrupt bourgeois law

The main two points to understand when studying what the communists say or do:

1. Lenin and his followers were the ultimate opportunists; they never let principles interfere with the practical matters of gaining and keeping political power.
2. "Do not look for logic where you did not put it yourself" - i.e., do not try to view whatever the communists say as some coherent political, sociological or philosophical doctrine.

IOW, whatever they say boils down to:

• we are right because we are The Communists,
• you are wrong because you disagree with The Communists.

This, of course, creates a problem when the opponent claims to be "The Communist" too (the primary examples are Bolsheviks vs. Mensheviks and USSR vs. PRC). Not to worry - just call the opponent a revisionist and win the argument.

Example

E.g., the Marxist-Leninist idea of a "just war" is that

• A war is just when it promotes the interests of workers
• Support of USSR is the only interests workers have
• Ergo:
  • any war fought by USSR is just
  • in any other war, whatever faction is supported by the USSR is just.

The above was, in fact, the official USSR position throughout its existence, I shit you not.

PS. When I was in college, our informal term for Marxism was "Mraksism", from "Mrak" - darkness.

PPS. One my favorite jokes: a guy comes out of the oral exam on Scientific communism with a huge smile on his face.

• His friends ask him: "did you pass? got an A?"
• He answers: "no, I failed!"
• They ask: "why are you so happy about?"
• He answers: "I am here - while my classmate was arrested right there!"