Casey assessed the overall appeal of the series, of Aubrey and Maturin, noting the "political sophistication", "a deeper sense of the culture of the age" and the early introduction in the series of "two strong women with quite different attitudes to life", Sophia Aubrey and her cousin Diana Villiers. The different specialty knowledge of each man, Aubrey with his full complement of nautical skills and Maturin the learned physician, naturalist and linguist, allows the author to have conversations where "From time to time the two men fill each other in expertly, briskly and even wittily, and the reader is the third-party beneficiary." A more generally appealing feature of the novels, perhaps what draws women to the series as well as men, was "the friendship between the two men", a plausible intimacy. Casey offered that readers can so easily enter this fictional world, because "O'Brian did the hard learning long ago and then began to write with fully justified assurance and pleasure."