Foucault sees the dynamics of power shifting in the Enlightenment. Before the eighteenth century, he argues, power manifested itself in being seen. The king was a king, in part, because he was a body who could be paraded before the people. He wore on his body the emblems of his power.
During the Enlightenment, however, power shifted more and more to the unseen. This can been be illustrated most fully in the idea of Jeremy Bentham's panopticon. This "modality of power" is expressed by invisibility. Bentham presents it in his vision of a prison in which there is a central tower from which a guard can see into all the prisoner's cells, the exercise yard, and so on and know what is going on without himself being visible to the prisoners. Because the prisoners know that at any moment they can be observed—but cannot see their observer or know if they are being watched at that particular moment—the invisible prison warden has the preponderance of power.
Foucault understands this as the power of the modern nation state. The powerful can observe without accountability. This is depicted in George Orwell's 1984 and has been the subject of much controversy in terms of computer surveillance of citizens in the twenty-first century.
Foucault was highly critical of this power modality.