David Hume begins by dividing all perceptions into impressions and ideas, establishing that every simple idea derives from a corresponding simple impression. The imagination combines these elements through the principles of resemblance, contiguity, and cause and effect, which serve as the cement of the universe of thought. Hume examines abstract ideas, space, and time, arguing against the infinite divisibility of extension and demonstrating that space and time are perceived only as the manner in which objects and successive events exist. The core of the work addresses knowledge and probability, where Hume proves that demonstrative reasoning applies only to pure mathematics and algebra, while matters of fact rely entirely on experience.
He famously demonstrates that inferences concerning cause and effect do not stem from rational insight into hidden powers, but rather from custom and the constant conjunction of events. Belief itself is defined not as an additional idea, but as a superior force and vivacity given to an idea through its relation to a present impression. Hume extends this psychological mechanism to explain the probability of chances and causes, showing how contrary experiences divide the mind's impulses. Finally, the author exposes the foundational role of human sentiment and animal nature in grounding our judgments, preparing the philosophical transition toward passions and morality.
