'The Critique of Practical Reason' by Immanuel Kant is a philosophical treatise written in the late 18th century. This work examines the foundations of moral philosophy and ethics, specifically focusing on how practical reason can determine the will and moral laws. Kant explores concepts such as freedom, duty, and moral law, aiming to establish a system where morality is grounded in the rational capacities of human beings rather than in empirical experiences or speculations.