The Essay on the reigns of Claudius and Nero is neither a political testament nor – as it was authoritatively written – the failure of a generation of intellectuals. It is not a plain apology of Seneca nor it is an autobiography of the shape-shifting Diderot. It is instead a rigorous thought of the theme around which the construction of the complex relationship between philosophy and despotic power, in different times and forms, had been revolving. The century of Diderot and the experience which the philosophes had given rise to, could not avoid being subjected to the final balance, bringing into play the experience of Seneca, but also taking into account the concepts of ‘time’ and ‘circumstances’. The final balance was bitter for both the philosophes and the despots, the latter being mostly unaware of the results achieved by the former. It is worthwhile repeating that in the meantime the widely held awareness of the need for overcoming the unacceptable legal, economic and social gap existing among strictly separated bodies within the same State enslaved solely to the privilege had been strengthened.