With Madness and Civilization: History of Insanity in the Age of Reason Michel Foucault produced a re-examination of the human relationship to madness and especially shed light on the effects of exclusion produced by various discourses on the madman. First, he offers a historical reading where the Middle Ages would constitute an ideal era where the madman, standing at the limit of the supernatural, would have been accepted. Then, he presents – starting from Descartes’ work – the separation between madness and unreason at the Classical Age. Finally, he evokes another rupture where a reifying medical science would assimilate the madman who becomes patient-object. However, it appears that Foucault didn’t conduct an absolutely accurate historical study. But, we show that this fact doesn’t reduce the strength of his thought and even makes it more alive. First, we will see why his book appears as a historical fiction (as writes Foucault himself). Then, we will show how this fictional nature produces truth. Lastly, we will identify – without forgetting to point out any potential negative consequences – how this truth has helped certain struggles, especially those of anti-psychiatry. These effects of truth led to see madness as an object of research that must be thought through the effects of power produced by society.