Nothing is more curiously enquired after . . . than the causes of every phenomenon. . . . [We] push on our enquiries, till we arrive at the original and ultimate principle. . . . This is our aim in all our studies and reflections. These words sum up David Hume's plan: To discover the fundamental principles at work in the nature and extent of human knowledge, and in so doing to gain a clearer understanding of our perception, ideas (e.g. of cause and effect), impressions, beliefs, passions, virtues, and vices. Hume's piercing critique and relentless analysis make this truly one of the most influential works of the Early Modern period.