A larger objection might be that this "great texts" approach to the history of political thought leaves out too many things. For several decades now, historians such as John Pocock have been arguing that what we need to study is the overlapping succession of different styles, idioms or "discourses" of political thinking — such as republicanism, which drew on many sources and developed a kind of political mindset that cannot be captured just by analysing (as Ryan does) a handful of great texts. Or take nationalism, for example. This is a major factor in modern politics, with ideological components of various kinds; but it slips through Ryan's fingers here, as he refers to Fichte and Herder only in passing, never even mentions Mazzini, and otherwise treats nationalism only in relation to the fascistic blood-and-soil nationalists of the early 20th century.

That omission of Mazzini prompts some other thoughts about the nature of the canon here — not just the parlour game of asking who's in or out, and who does or does not deserve to be, but also some larger questions about what a canon is and how unhistorical it might be. Ryan's list of the great and good is a fairly traditional one, though some of the figures in it are surprisingly downgraded. (Bentham, for example, an inventive and influential thinker, is dealt with in just a couple of rather breezy pages.) Immanuel Kant is a major casualty; readers get to know very little about him, except when they are told how some of his ideas were adapted by Hegel. The inclusion of a substantial chapter on the American founders — principally Jefferson and Madison — is, on the other hand, a good thing, not only for prospective sales of this work as a textbook in US universities, but also for British readers, who still tend to underestimate the depth and seriousness of those writers' debates on politics and the state. 

Followers of Jonathan Israel, who has claimed that the modern world was created by Spinoza, will be disappointed to find no account of Spinoza's political thought at all; but even those of us who don't follow Jonathan Israel may think that Spinoza's views on freedom, religion and republican government deserved some treatment. Certainly they merited more space than the political observations of the late medieval writer Christine de Pizan, which, described (accurately) as "short and slight" and "intellectually undemanding", take up five pages here. One hesitates to accuse Alan Ryan, of all people, of tokenism, and perhaps the real explanation is that US university courses have taken Christine de Pizan to their hearts; but I would rather read five pages about Mary Wollstonecraft (mentioned only in passing in this book) any day of the week.

As for the larger question about whether a canon is an artificial and unhistorical device: well, it is obviously inadequate when judged by the standards of "total history", as it has to leave out a lot of the history of thinking that happened in between the writing of those canonical texts. But, as Ryan points out repeatedly, the canon cannot be dismissed as just a modern projection onto the past; it developed over time as a historical phenomenon in its own right, as Aquinas read Aristotle, Rousseau read Hobbes, and so on. One of the most important developments in this field in recent times has been the new emphasis on the political contexts of these writings; since the work of Quentin Skinner, we have known that even the most abstract works of political theory need to be looked at as interventions in the politics of their time, and that some aspects of their meaning will remain obscure if we do not do this. But that is not an objection to the concept of a canon, and was never meant as a denial that some texts are more philosophically important than others; it certainly did not stop Quentin Skinner himself from writing about two of the most canonical figures of all, Machiavelli and Hobbes.