I'm not sure how to write this review, other than to give my overall impression of the book as a Kant-scholar and philosophy nerd. I found Kuehn's biography of Kant both well written and remarkably interesting, and he does us a great service to help us to understand the man whose ideas have been so influential.
Kant was a remarkable phenomenon. Spending his entire life in Königsberg, a moderately prosperous trading city on the Baltic and largely isolated outpost in the east of Prussia, Kant was born to a Pietist bridle maker. His father made just enough to get by, and because of their religious connections, young Kant was educated in Pietist schools. He never married and all evidence suggests that he spent his entire life a virgin, though, it would seem, many women found him to be a handsome and eligible bachelor. Kuehn provides significant and rare insight into Kant's youth and pre-Critical career, focusing on his personal, professional, and intellectual relations, as well as his position within Prussian society.
I got a sense that Kuehn is attempting some sort of revisionism with this biography, though I think he successfully argues for why this is necessary. Kant rose to great fame when he was 57 (when the first edition of the Critique of Pure Reason was published), and continued to publish philosophically influential works right into his 70s. (He died just shy of 80.) Because of his "late bloom," earlier biographers offered anecdotes of Kant as his contemporaries knew him, which was, by then, as an eccentric, stubborn old man, a strong moralist, and at times a misogynist. Kuehn attempts to revise this picture, depicting a side of Kant that is more human and emotionally complex.
I noted that some things were missing. For instance, there was until a few decades ago a popular theory that Kant descended from Scottish merchants who settled in the trade-city of Königsberg. (Cant (sic) is a Scottish name.) This theory is thin enough not to grant much credibility, and trivial enough to be of little consequence; however, since so many scholars often claimed this in their brief biographical sketches of Kant, I would have expected Kuehn to have something to say about it. (In a way, he said something about it, asserting that Kant's not-too-distant paternal ancestors were born not in Königsberg, but in Bavaria.)
Moreover, some of Kuehn's remarks seem largely based on speculation and little based on substantial evidence. For example, Kuehn portrays Kant as publicly a theist (of sorts) but privately an atheist. While much has been written about Kant's views of religion, which are heretical at best and hostile at worst, I don't think we can say so easily that he was personally an atheist as opposed to an agnostic or deist. The fact that he was dismissive of religion (he counted prayer as superstition and looked down on rituals) and avoided the church does not indicate atheism. Also, given what he does say about religion (even when he doesn’t seem tied into knots by censors), I don't think we can label him an atheist so simply.
Overall I think this was a good read. If you're just into philosophy and not into history, however, I doubt you'll much enjoy it. Kuehn doesn’t spend much time discussing Kant's philosophy, focusing instead on his personal life and how it fits into the milieu of 18th century Königsberg.