<DIV>Martin Heidegger's (1889-1976) influence has long been felt not just in philosophy, but also in such fields as art, architecture, and literary studies. Yet his difficult terminology has often scared away interested readers lacking an academic background in philosophy. In this new entry in the <I>Ideas Explained</I> series, author Graham Harman shows that Heidegger is actually one of the simplest and clearest of thinkers. His writings and analyses boil down to a single powerful idea: being is not presence. In any human relation with the world, our thinking and even our acting do not fully exhaust the world. Something more always withdraws from our grasp. As Harman shows, Heidegger understood that human beings are not lucid scientific observers staring at the world and describing it, but instead are thrown into a world where light is always mixed with shadow. The book concludes with a comprehensible discussion of the philosopher's notoriously opaque concept of the fourfold.</DIV>