Scientific socialism, a term popularized by Friedrich Engels in 1800, refers to an application of socialism that is scientific in nature, and therefore follows the philosophy of marxism as science is inseparable from socialism, and socialism is inseparable from science. The phrase rose to prominence to distinguish from utopian socialism, which has become a pejorative used to imply naïveté.
Main article: Marxism
The philosophy of Marxism is materialism. Materialism is the philosophical outlook that claims matter is the fundamental substance of nature and that everything that exists, including thoughts and consciousness, is the result of material interactions.
But Marx, while refining materialism, was the first to join it to Hegel's dialectics. It then became possible to understand why the world changes (why capitalism became the dominant mode of production, why whole civilisations stopped existing...) and how. Lenin wrote:
Just as man’s knowledge reflects nature (i.e., developing matter), which exists independently of him, so man’s social knowledge (i.e., his various views and doctrines—philosophical, religious, political and so forth) reflects the economic system of society. Political institutions are a superstructure on the economic foundation. We see, for example, that the various political forms of the modern European states serve to strengthen the domination of the bourgeoisie over the proletariat.
Having recognised that the economic system is the foundation on which the political superstructure is erected, Marx devoted his greatest attention to the study of this economic system. Marx’s principal work, Capital, is devoted to a study of the economic system of modern, i.e., capitalist, society.
It was originally Adam Smith and David Ricardo who wrote the most, and probably the first, works on economical theory. Their work would become the prevalent basis for economics in much of the western world. In particular, they are the ones who came up with the labour theory of value, which was the prevalent theory of value in the world until it started inevitably leading to Marxism, which led neoclassical and neoliberal economists to come up with alternative theories so that they could justify bourgeois exploitation over the proletariat.
Marx continued working on the labour theory of value and developed it consistently. He showed that the value of every commodity is determined by the quantity of socially-necessary labour time spent on its production (that is, the average amount of time it takes to produce such a commodity).
Where the bourgeois economists saw a relation between things (the exchange of one commodity for another) Marx revealed a relation between people, and as such he was able to prove the concept of surplus value, which in class society is being stolen by the oppressive class for their personal enrichment.
The third fundamental component of marxism is the class struggle. Studying from the last days of feudalism and its eventual replacement by capitalism, Marx understood which social forces are responsible for change and why. The bourgeoisie was progressive compared to the feudal lords and monarchs.
Why did the bourgeoisie enter in conflict against the nobility? Because the two were contradictions, and one was prevented from growing as long as the other existed. The bourgeois waged wars on the aristocracy to establish themselves as the dominant social class (see for example the French Revolution of 1789), as the nobility would never have willingly given up their power because it was not in their class interest. Lenin concludes:
Marx’s philosophical materialism alone has shown the proletariat the way out of the spiritual slavery in which all oppressed classes have hitherto languished. Marx’s economic theory alone has explained the true position of the proletariat in the general system of capitalism.
According to Lenin, it is necessary for the proletariat to understand the philosophical and economical theories of marxism to understand the class struggle and their place in it.
Scientific socialism is based on the principles of science. In this way, it is able to evolve with the times and adapt itself to the material conditions of any society.
Moreover, as materialism is ultimately the scientific conception of the world, and marxism is the application of materialism to the class struggle, the two become inseparable: there can not exist any socialism without science.
Much like a scientific experiment, marxism allows one to declare hypotheses and test them out. Marxism as a philosophy evolves with the people who practice it, and does not stay rigid (and therefore becomes irrelevant). For example, while kulaks were an oppressive class in Tsarist Russia, they were not strictly bourgeois or proletarian. Likewise, there wasn't really a proletariat in 1900s Russia, as much of the population worked as peasants (serfdom was only abolished in 1861). Understanding these social classes and their revolutionary potential (their interests and where they placed on the class struggle) was instrumental in establishing socialism in Russia.
The components of marxism, coupled with this scientific approach, form scientific socialism: a guiding principle for socialist societies.
Utopian socialists where the first socialists, and some still exist today as the word has taken a larger meaning. Utopian socialists are idealists ; they believe that ideas create matter and that achieving socialism only requires everyone to have the right ideas.
As such their struggle is shallow in nature. Some of the early utopian socialists, for example, believed that if they created more efficient factories, traditional factory owners would be put out of business and the workers would be emancipated. Or that perhaps if they created alternative cities where the workers would not be exploited, they could convince the bourgeoisie that it was not necessary to exploit their workers.
They tested these ideas and found that they did not work, but put the blame on the workers themselves or, as they were idealists, on God: if they are not able to change the world with their ideas, then it must be because the world is not yet ready for them, and so it must be God that prevents their ideas from flourishing.
Utopian socialists failed because as much as they rejected capitalism on moral grounds, they did not understand the underlying mechanics that drove it and made it the dominant mode of production in society. They did not understand marxism and its three components, which form scientific socialism.
Idealists will ultimately justify their philosophy by arguing in favour of a higher power. For this example we pick the Abrahamic God, but this can work in any religion (be it monotheist, polytheist, or even animist). God is non-falsifiable (it is impossible to prove God does not exist), requires no burden of proof (everyone knows God exists, as religions exist everywhere in the world), and more importantly: belief in God does not require any research be made in those two aspects. Here it becomes apparent that idealism is not scientific -- it is in fact opposed to science and it is inseparable from religion.