"All human activity is prompted by desire." This seems like a pretty inaccurate statement. He's explicitly saying that moral actions are also desire-driven, be

"All human activity is prompted by desire." This seems like a pretty inaccurate statement. He's explicitly saying that moral actions are also desire-driven, because if we didn't desire to do the thing, we wouldn't do it. But we know we don't wish to do the things we sometimes do, because we have internal conflict over it; if we wished to do it, it wouldn't be hard to make ourselves do it. Clearly we know the things we "wish" to do, because we do them quickly and freely without internal pain. Other things we "don't wish" to do, we do have internal pain over and do take more effort to make ourselves do. So Bertrand's word "desire" is really just a synonym for "motivation". If you said "All human activity is prompted by motivation," then that wouldn't work for human activity prompted by, say, heuristics. We now know that much of human beings' immediate actions are actually just an automatic response to pattern-matching algorithms in the brain. Those actions can't be driven by desire, because they're almost subconscious; it's not what we "wish for", it's what the body immediately responds to in order to keep itself alive in a dynamic and dangerous environment. Therefore, all human activity is not prompted by desire, but by whatever kooky biological processes make up our brains and control our actions, voluntary or involuntary. But that's not a very sexy quip for a talk :-)