P.'s monograph traces the use of the term voluntas in Cicero's extant works, with a view to understanding how Cicero conceived of the individual human ‘will’ and the ‘will’ of the populus Romanus.

Part 1 (Chapters 1–5, dealing with the practice of voluntas) argues that, in relation to the individual will, Cicero substantially extended the reach of the term voluntas, so that, in addition to its use to denote a wish or intention simpliciter, it might denote more specifically a rationally-derived will to act in a particular way or a durable disposition entailing, for example, goodwill towards a particular person or cause. In discussing individual voluntas, P. draws substantially on De inventione, on Cicero's speeches and on his private letters. He notes that Cicero also applied the term voluntas populi to the collective will of the populus Romanus. P. finds in Cicero's speeches of the 50s bce and in De re publica and De legibus a novel account of how the libertas of the people could be reconciled with limits on its political rights, and, in this regard, P. attaches significance to the role of voluntas populi in Cicero's thought.

In Part 2 (Chapters 6–8, dealing with the philosophy of voluntas) P.'s focus shifts to Tusculanae disputationes, Academica, De fato, De finibus and De officiis. P. finds that Cicero proposed a different account of the functioning of the soul from those advanced by Plato, Aristotle and the Stoics. Indeed, P. suggests that Cicero effectively invented the idea of the individual will. And, P. notes, Cicero explored the possibility of free will, using the phrase libera voluntas. Finally, Cicero proposed in De officiis that, of the various personae (roles) that a single individual fulfils in life, whilst some derive from an individual's circumstances, one is chosen according to individual voluntas. An epilogue discusses Cicero's influence on later philosophical treatments of the will and free will, from Augustine to the founding fathers of the USA.

There is much to commend in P.'s work: its exploration of the tension between Cicero's principled attachment to Rome's republican institutions and the pressure he apparently felt to resort to less principled means to protect them; its attractive account of the way in which Cicero's life and career shaped the evolution of his moral and political understanding; and its compelling account of the subtleties of relationships among the senatorial elite in the late republic, invoking modern conceptions of ‘powermapping’ to explain Cicero's attempts to identify and utilise the voluntas of those who wielded political power or influence.

P. also draws on a commendably wide range of texts to support his case and offers insightful analyses of various individual passages. For example, in comparing Cicero's De inventione to the contemporary Rhetorica ad Herennium, P. offers a particularly good account of the superiority of Cicero's treatment of the arguments available to an orator who wishes to contend that a legal text should be interpreted according to its written terms (scriptum) or, alternatively, its draftsman's intention (voluntas).

Yet P.'s overall methodology raises various concerns. His focus on examining the use of just one word, voluntas (and occasionally its cognates voluntarius and velle), risks investing too much in this one word. Often Cicero couples voluntas with other nouns. Most often voluntas signifies simply a wish or an intention (what a person wishes or intends to do or see done), while the coupling of voluntas with iudicium or consilium discloses the kind of voluntas involved: a voluntas shaped by judgement or entailing commitment to a project or plan. P.'s focus on voluntas risks obscuring the significance of other terms in conveying the totality of Cicero's meaning. A similar risk arises where individual texts are read in isolation from their legal context. As P. notes, the voluntas expressed in a testamentum outlasts the testator's death. But the lasting effect of a testamentary expression of voluntas derives from its operating within a legal system in which validly executed, unrevoked testamenta are given effect after the testator's death as the binding expression of his voluntas in relation to the disposition of his estate. Similarly, a lex of general application takes effect, within a wider legal system, as the legislator's formal pronouncement as to how all future cases falling within its scope should be determined, thereby conferring lasting effect on the legislator's voluntas. But these usages of voluntas do not warrant an inference that, in other contexts, voluntas will also carry a suggestion of the durability of a wish or intention, the rationality or planning that underlies it, or its imposition of obligations on others to observe it.

P. also appears to attach unwarranted significance to voluntas populi in the argument of De re publica. Cicero's model res publica is characterised by the optimal balance (aequabilitas) it strikes among magistrates, senate and people, so that government is entrusted to those best suited to it, while the people enjoy such rights as will confer on them just enough libertas to ensure their continued support for the system. P. provides a compelling account of the extent of the libertas that the generality of Roman citizens will enjoy by virtue of their right to elect magistrates, the structuring of the electoral assembly in a way that gives greater weight to the votes of citizens of higher rank, and the expectation that magistrates, once elected, will act wisely in pursuit of the people's interests: what is done by magistrates in the people's name is done in pursuance of the people's voluntas. But the terminology of voluntas populi plays a relatively small part in Cicero's presentation: other terms are used more often than voluntas/velle to denote the people's expression of its will. They include, for example, deligere, permittere, ferre, flagitare, asciscere, iubere, creare, concedere, cedere, pati and parere. Moreover, the people's libertas is also protected by mechanisms that are arguably somewhat removed from the expression of voluntas populi: citizens enjoy individual rights of provocatio and the protection of tribuni plebis, as key elements of the consensus iuris that holds the res publica together, by making the whole acceptable to citizens generally. By its focus on voluntas populi P.'s analysis risks elevating the significance of this term and diminishing the significance of other aspects of libertas.

In Part 2's examination of Cicero's philosophy of the human soul, P. finds in Tusculanae disputationes a novel conception of ‘willpower’. Cicero adopts the term voluntas to translate the Stoic βούλησις. P. suggests that, in doing so, Cicero imports attributes of voluntas that P. has identified as attaching to it in Cicero's other works and in earlier Latin texts. Thus P. earlier found in voluntas an on-rushing quality: it is desire-in-motion. P. cites Varro's etymology of voluntas, which drew an association with volare (‘to fly’). Accordingly, P. argues that Cicero's statement at Tusculanae disputationes 4.12 (voluntas est quae quid cum ratione desiderat) is to be read as suggesting that voluntas is not merely a belief, but a power – willpower – a durable force-in-motion. But the notion of a motive force of some kind was arguably already implicit in the Stoic βούλησις (M. Frede, A Free Will [2011], pp. 20–1). Cicero's reasoning here is obscure and potentially incoherent (M. Graver, Cicero on the Emotions [2002], pp. 134–9). P. cites alternative analyses of this passage, but could usefully have addressed them more fully in advancing his own interpretation.

In short, P.'s monograph offers much that is of great interest and great value, but its overall method is arguably not always ideally suited to its object.