For some decades now, contemporary Western scholarship focusing on the history of philosophy in the Islamic world has increasingly been turning its attention toward the period that followed the central figure of Avicenna. Frank Griffel is one of the leading actors of this trend, having already published a first pivotal monograph on Abū Ḥāmid al-Ghazālī's philosophy and theology and its contextualization in the history of Islamic thought (Griffel, Reference Griffel2009), and now offering a rich and in-depth account of the development of philosophy after al-Ghazālī during the 6^th/12^th century in The Formation of Post-Classical Philosophy in Islam. In it, he provides not only a thorough and fascinating characterization of the historical, religious, and social conditions that played a role in what he understands as being a transformative process that took place at this time in the philosophical discourse in Islam but also a description and critical analysis of its methods, theories, and claims.

The book is structured in three parts. Part I begins with a detailed geographical, historical, and institutional contextualization of the discipline of philosophy in the Eastern territories governed by Muslim rulers in the mentioned period. It emphasizes, in particular, the way in which the shifts in the political power observed in the 6^th/12^th century following the Mongol invasions had an impact on the reorganization of the intellectual centres in the Eastern Islamic world. It then moves on to a discussion about how philosophers and religious and legal scholars came to perceive and depict philosophy in their works, and how this influenced the lives of philosophy scholars themselves.

Part II is concerned with the biographies of some of the most important 6^th/12^th century philosophers in the Islamic world and their works. It pays particular attention to al-Lawkarī, ʿUmar Khayyām, al-Shahrastānī, Abū l-Barakāt al-Baghdādī, Sharaf al-Dīn al-Masʿūdī, Ibn Ghaylān al-Balkhī, Majd al-Dīn al-Jīlī, Shihāb al-Dīn al-Suhrawārdī, and Fakhr al-Dīn al-Rāzī. Thinkers are classified according to their position in relation to the central figures of Avicenna and al-Ghazālī (Avicenna's critic), that is, according to whether they were part of the current that Griffel designates as ‘Avicennism’ or to ‘Ghazalianism’. Abū l-Barakāt al-Baghdādī, although influenced by al-Ghazālī in his criticism of Avicenna, is understood as an ‘outsider’, both because of the particularity of his religious and educational background (Jewish) and the originality of his critique. Fakhr al-Dīn al-Rāzī is considered the point of culmination of the philosophical developments in the post-classical period.

Part III is the most extensive and argumentative part of the book. It looks at the methodological and theoretical developments that characterize the ‘genre’ of post-classical philosophy in the Islamic world, which is, according to Griffel, labeled by the Arabic term ḥikma. It focuses mainly on the works of al-Rāzī but also includes key chapters on the specific contributions of al-Masʿūdī and al-Baghdādī. The analysis of philosophical topics concentrates especially on epistemology and metaphysics and aims to point out the main innovative claims made by post-classical authors.

The book concludes with an epilogue discussing the relationship between philosophy and Islamic rationalist theology (kalām) in the post-classical period, based on the example of Fakhr al-Dīn al-Rāzī, who stands out as the main protagonist of the book. It also includes two appendices: the ‘List of Avicenna's Students and Scholars Active in the Sixth/Twelfth Century’, and the English translation of Eşref Altaş’ relative chronology of Fakhr al-Dīn al-Rāzī's works, originally published in Turkish (Altaş, Reference Altaş, Türker and Demir2013).

Griffel's most significant claim in the first part of the book is the distinction between the labels of falsafa and ḥikma and the respective derived terms faylasūf (pl. falāsifa) and ḥakīm (pl. ḥukamāʾ). He argues that, in the 6^th/12^th century, the term falsafa, which previously stood for philosophy, acquired a more specific meaning, namely that of ‘Avicennism’, i.e., the philosophical system promoted by Avicenna. This new meaning emerged, according to Griffel, as a result of al-Ghazālī's identification of this tradition with a particular set of teachings associated with Avicenna in his famous The Precipitance of the Philosophers (also known as The Incoherence of the Philosophers) (pp. 77‒79). Consequently, also the term faylasūf, meaning ‘philosopher’, became the equivalent of ‘Avicennan philosopher’, that is, a follower of Avicenna. What is more, Griffel maintains that following al-Ghazālī's critique, falsafa and faylasūf received a pejorative connotation, in the sense that they became connected with the idea of unbelief (kufr), based on the denial of some of the fundamental doctrines of Sunni Islam (in particular of (1) the temporal creation of the world, (2) God's knowledge of particulars, and (3) bodily resurrection, i.e., the three doctrines targeted by al-Ghazālī's Precipitance), as well as with a morally reproachable behaviour resulting from the negligence of religious duties, such as drinking wine. Griffel goes so far as to claim that this new understanding of falsafa gave it the sense of a quasi-religious movement. He makes a compelling case by adducing evidence from Judah Halevi's portrayal of the falāsifa in his Book of Kuzari and al-Shahrastānī's inclusion of falsafa in his Book of the Religions and Sects, as well as his attribution of certain teachings contrary to the Sunni creed to some of its scholars (p. 79ff.). With this conclusion, it is easy for Griffel to argue that, in order to avoid the negative undertone of these terms, ḥikma became in the 6^th/12^th century ‘the new technical term for philosophy’, and, likewise, philosophers preferred to call themselves ḥukamāʾ, rather than falāsifa (p. 96ff.).

This is an original and attractive interpretation of the development of these designations. However, Griffel's hypothesis also raises several problems on the argumentative level. It seems to me that the terms falsafa and falāsifa in the 6^th/12^th century were not exclusively used to refer to Avicennism but also to philosophical claims brought forth by other authors in the philosophical tradition, such as al-Fārābī, and Plato, and even Galen, without necessarily conveying a negative connotation. Al-Ghazālī himself mentions al-Fārābī by name together with Avicenna in the introduction of his Precipitance as one of the targets of his refutation. In works by Fakhr al-Dīn al-Rāzī, one can find Plato and Galen mentioned under the label of falāsifa, even in cases where he does not disagree with their position on a certain topic (e.g., al-Rāzī, Reference al-Rāzī and al-Baghdādī1990, vol. 2, p. 282). Thus, it seems that more clarification is needed to assert a radical and systematic shift in the understanding and usage of this term as meaning ‘Avicennism’. Moreover, the fact that the falāsifa are included in al-Shahrastānī's Book of Religions and Sects does not necessarily entail that the author considered philosophers as members of a ‘quasi-religious movement’. Even if one should agree that al-Shahrastānī presents the falāsifa as a dogmatic group, there does not seem to be an essential connection with the idea that they formed a social organization with a set of beliefs and religious practices associated with those beliefs. This does not undermine Griffel's overall argument for the distinction between falsafa and ḥikma, but it does call for a more nuanced approach to it.

Finally, the central thesis that Griffel proffers in the last part of the book, and which deserves particular attention for scholars interested in the works of Fakhr al-Dīn al-Rāzī, is that the latter developed a certain ‘tolerance of ambiguity’ with regards to some theoretical claims. Griffel borrows this concept from Thomas Bauer's A Culture of Ambiguity: An Alternative History of Islam, in which the author claims that Islamic culture and societies in the pre-modern period were more open to accepting and celebrating disparate truth claims than after European modernity became influential in their discourse (Bauer, Reference Bauer, Biesterfeldt and Tunstall2021). Griffel tests this thesis on how al-Rāzī came to defend different and even contradictory claims on the understanding of God's act of creation in his works of theology and philosophy. He eliminates the hypothesis of a development, previously suggested by scholars such as Paul Kraus and Joseph van Ess, by looking at the chronological order of his writings, which is not coherent with the doctrinal shifts observed. Consequently, he draws the broad inference that these derive from a general attitude of tolerance to concurring views. At first, this strikes the reader as an interesting and creative explanation for the perplexities scholars have faced in interpreting al-Rāzī so far. Yet, it may not appear sufficiently satisfactory to an attentive reader of al-Rāzī, who may argue that the discrepancies in argumentation and opinion found in his different works should rather be understood as a life-long process of research to find the best explanation for certain questions and the strongest evidence for certain claims. The problem of the essence of the human soul is a good example. In several of his works of kalām, al-Rāzī holds a materialistic view of human nature (al-Rāzī, Reference al-Rāzī and Muḥammad2009, pp. 382‒83; Reference al-Rāzī and Fūda2015, vol. 4, pp. 79‒80), whereas, in his philosophical works, he supports the idea of a body-soul dualism (al-Rāzī, Reference al-Rāzī and al-Baghdādī1990, vol. 2, p. 359ff.). However, even if these disparate answers to the question may seem at first contradictory, the premises and arguments that al-Rāzī uses throughout his works appear to be consistent: he goes back to arguments that he previously used to validate one or the other option, proposes solutions to problems encountered in previous arguments, and his theological position, which at first seems to follow a univocal physicalist approach to human nature shows, in later works, a considerable influence of the philosophical dualism (al-Rāzī, Reference al-Rāzī and al-Saqqā1986, vol. 2, pp. 59‒60; Reference al-Rāzī and al-Saqqā1987, vol. 7, p. 141ff.). Reducing the differences and similarities found across these different works to a tolerance of ambiguity would neglect the systematicity and the developments that can be reconstructed in al-Rāzī's argumentative methods and claims. In fact, throughout the discussion, Griffel barely addresses Ayman Shihadeh's crucial contribution to this debate (more recent than that of Kraus and Van Ess), and in particular, his thesis that some of al-Rāzī's ethical teachings underwent a development, while certain ideas can be found throughout almost his entire oeuvre (Shihadeh, Reference Shihadeh2006). It remains, however, that Griffel's hypothesis triggers fundamental questions and paves the way for further research on the challenging case of al-Rāzī's.

In sum, this book is admirable in its comprehensive approach and meticulous analyses, which draw on an impressive amount of sources and literature. It is undoubtedly one of the most extensive and crucial contributions in the field of intellectual history in the Islamic world. It constitutes essential reading not just for scholars in Islamic studies but also for those interested more broadly in the history of philosophy, making a significant move towards expanding the philosophical canon to include authors part of this tradition of Islamic thought.