It is difficult to exaggerate the importance of Michelle Grier's book. It could be said that it constitutes the most important insight into Kant's Critique of Pure Reason since it was published. It seems to have been recognized as such by contemporary scholars. One of the most prominent, Henry Allison, in his extensively revised book, Kant's Transcendental Idealism, owes, according to its author, not just new ideas about but an entirely new and different understanding of Kant's philosophy. An Amazon search of citations of Prof. Grier's book shows that prominent Kant scholars have taken note of her work. Her thesis, in its usual description, sounds tame. She argues from the Kantian text that what Kant calls illusion is and was meant by him to provide the fundamental understanding of what human reason is: illusion is not a deplorable mistake or sad limitation, but the enticement toward which reason must strive, giving it direction as well as energy. She shows in detail how this interpretation makes specific sense of the puzzles that have plagued or mislead scholars to date. Kant's work, one should not forget, is titled "The Critique of Pure Reason", and so a clarification, especially one that is on the one hand historically so recent but nevertheless on the other hand absolutely convincing and solidly right, is highly extraordinary. Her telling us what Kant was driving at when no one before her saw it makes her book a wonder glittering brightly among the many good commentaries on Kant's thought.