The core of Foucault's thought can be seen from his famous saying - "Man dies".

His "man is dead" follows Nietzsche's "God is dead". Nietzsche criticized the theocratic power that suppressed human reason in the Middle Ages, while Foucault criticized the worship of subjectivity and essentialism of humanism in the industrial age. Because over-emphasis on human subjectivity denies the existence of human beings as complex and diverse personalities, and in the pursuit of essentialism, many so-called non-essential factors are extracted due to the pursuit of essence, and these factors are precisely The most diverse part of human nature. Therefore, Foucault believes that "man" in this era has died, and should be replaced by a postmodern state that emphasizes plurality of personality, anti-essence and centerlessness.

His major works such as "Madness and Civilization", "The History of Sexuality", "Discipline and Punishment", etc. all run through this core idea.