Critical theory aims to emancipate society rather than merely describe it, as traditional research does. The fundamental principles of this engaged science were first outlined by Horkheimer in his famous essay from 1937 in the Journal for Social Research. The afterword helps to understand the complex implications of this simple idea. Additionally, it highlights the main criticisms of Horkheimer's arguments and their further development within the Frankfurt School, tracing the enduring legacy of this crucial, groundbreaking text to the present day.