Big thinkers make for big targets and they don't come much bigger, physically and intellectually, than Daniel Dennett. The tall, 71-year-old philosopher looks every inch the enthusiastic sailor he is, with his white beard and broad torso. With his mild-mannered, avuncular confidence, he comes across a man who could calmly fend off an assault or two. That's just as well, since as a leading cheerleader for Darwin and atheism, he is as much a bete noire for their opponents as a hero for their advocates.

Dennett is in London from his native Massachusetts talking to me about his latest book, Intuition Pumps and Other Tools for Thinking. It's a kind of greatest hits collection, pieced together from mainly previously published work to present both a summation of his central ideas about meaning, consciousness, evolution and free will, and to share some of the philosophical tools he has used to craft them. "After half a century in the field I've got some tricks of the trade which I'd like to talk about," he says.

His critics agree, to the extent that they see him as a clever philosophical trickster. Yet time and again it seems the best way to understand Dennett is to understand why so many criticisms miss their targets.

Most assaults are variations on the theme that Dennett takes a too narrowly scientific worldview. The late Stephen Jay Gould, for instance, coined the "shocking" terms "ultra-Darwinist" and "Darwinian fundamentalist" to hurl at him. Yet Dennett has consistently resisted the crude extension of scientific thinking into areas where it does not belong. Nowhere is this more evident than in the issue of free will, which he describes in the book as "the most difficult and the most important philosophical problem confronting us today".