David Hume, <i>An Enquiry Concerning Human Understanding</i><p>It showed me that intellectual curiosity doesn't need to be coupled with abstruse language, that in fact unclear language is not a sign of deep thought, but more likely unclear thought. It showed me that being an optimist isn't stupid, that it's an art and that gloom is not an inevitable consequence of intellect. I was suffering from depression back then. It took me 10 more years to win the battle, but I did it. It was all more about how this book was written, rather than what was written in it.<p>Tony Judt, <i>Past Imperfect: French Intellectuals, 1944-1956</i><p>Tony Judt, <i>The Burden of Responsibility: Blum, Camus, Aron, and the French Twentieth Century</i><p>Czesław Miłosz, <i>The Captive Mind</i><p>Raymond Aron, <i>The Opium of the Intellectuals</i><p>Those books taught me that there are quite a few secular religions to be beware of, with all the associated dangers and indeed opium for the mind. They were written with the example of Marxism, but this lesson can be generalised to other ideas, which explain away everything about life and bring a prophesy of things to come. It taught me that the religion I left behind when I was young is not the end, but there are more things to be vigilant about, lest your critical mind becomes anaesthetised and subjugated by the current intellectual orthodoxy.<p>Judith Butler, <i>Gender Trouble</i><p>A truly insane book. Prior to reading it I thought that the criticisms coming from "the other side" were caricatures. After reading this book I've known that there truly are people denying the reality of biology and making all sort of twisted reasonings you would have never dreamt of. The political movement associated with this book doesn't let it slip at first, but when I confronted core members of this movement (responsible for most of the political messaging in the press etc.) in my country it turned out that they actually believe that stuff. It disillusioned me about the sort of nonsense people can seriously believe, while carefully not admitting it at first.