Scientists and philosophers spent a century arguing over correlation and causality, but Judea Pearl makes a major effort here to put the study of cause and effect on a firm scientific basis. His work explains how we can know easy things (was it rain or a sprinkler that made a sidewalk wet) and how to answer hard questions, like whether a drug cured an illness. Nothing is off limits, and so Pearl tackles the Bayes Theorem, the Monty Hall Problem, and the Lord Paradox, while finding a philosophical way of proving that cigarettes can cause cancer and pondering the misleading question, "Would Kennedy be alive if Oswald hadn't killed him?"