This book provides a commentary on Kant‘s „Postulates of Empirical Thought in General“. It investigates Kant‘s entire theory of modal concepts from the mid-1750s up to the publication of the Critique of Pure Reason. It was in this work that Kant first answered the question „What is an object?“. In the process, he responded to other theories of objectivity native to the 18th century: rationalism, empiricism, idealism, and skepticism.