Abstract: Marx's critical research approach has shifted, from its early insight into legal, philosophical, and moral topics, to the later critical research on political economy concerning with real social and economic relations. Correspondingly, Marx's focus on problem consciousness, with the progress of his research approach, has also undergone changes. These problem consciousness, irrelevant to each other, revolve around Marx's core research approach, namely the concept of human liberation. Such concept has evolved from the early abstract freedom and equality to a comprehensive freedom based on social ownership of means of production, and then a realistic equality based on the principle of transcending feedback justice in the context of the new historical perspective. Political philosophy thinking runs through the critical study of Marxist philosophy and political economy. With this thread as a clue, the inherent continuity and systematicity of Marx's research approach in the problem domains of different periods and fields unveil.

Key words: Marx, income from labor, dual-objectivity relationship, critical thinking