Pyotr or Petr Yakovlevich Chaadayev (; also spelled Chaadaev, or Čaadajev; 7 June [27 May Old Style] 1794 – 26 April [14 April O.S.] 1856) was a Russian philosopher. He was one of the Russian Schellingians. Chaadayev wrote eight "Philosophical Letters" about Russia in French between 1826 and 1831, which circulated among intellectuals in Russia in manuscript form for many years. They comprise an indictment of Russian culture for its laggard role far behind the leaders of Western civilization. He cast doubt on the greatness of the Russian past, and ridiculed Orthodoxy for failing to provide a sound spiritual basis for the Russian mind. He extolled the achievements of Europe, especially in rational and logical thought, its progressive spirit, its leadership in science, and indeed its leadership on the path to freedom. The Russian government saw his ideas as dangerous and unsound. After some were published, they were all banned by the censorship process. Because there was nothing to charge him with, Chaadayev was declared legally insane and put under constant medical supervision, though this was a formality rather than a real administrative abuse. Biography Chaadayev was born and died in Moscow. The familty name of the probably derives from the Turkic word Chaʿadai, with the name deriving from Chagatay, the second son of Genghis Khan. (The Mongol name Chagatay means "bold", "honourable" or "true".) After leaving Moscow University without completing his course in 1812, he entered the army and fought against the 1812 French invasion of Russia. Chaadaev's first-hand observation of Emperor Alexander's reaction to the in the Semenovsky regiment (in which Chaadayev had previously served) in October 1820 may have led to his resignation from service in December 1820. From 1823 to 1826 he travelled in Europe, so he was out of Russia during the 1825 Decembrist insurrection, though he was questioned on his return about his connections with many of the Decembrists. These connections may have contributed to his failure to find a position in the new administration of Emperor Nicholas I (). Chaadayev befriended Alexander Pushkin (1799-1837) and became a model for Chatsky, the chief protagonist of Alexander Griboyedov's play Woe from Wit (1824). During the 1840s Chaadayev was an active participant in Moscow literary circles. Philosophy The main thesis of his famous Philosophical Letters was that Russia had lagged behind Western countries and had contributed nothing to the world's progress and concluded that Russia must