The concept of ‘imagination’, celebrated in contemporary discourse as a cornerstone of human creativity and innovation, contrasts starkly with its more nuanced historical interpretations, especially in the classical period where it was encapsulated by the term phantasia. Historically, phantasia was perceived as a passive phenomenon – a mere by-product of sensory experiences. Plato, for instance, viewed it as an element of perception possibly supplemented by judgement, whereas the Stoics engaged with it primarily to debate its reliability in the acquisition of knowledge. Within this broad ancient discourse, Aristotle's conceptualization of phantasia stands out prominently; he strives to distinguish it clearly from both sensory perception and intellectual reasoning. The book reviewed here presents a thoughtful argument that Aristotle developed an active and productive notion of phantasia, specifically to elucidate the cognitive underpinnings of geometry, thereby bridging the conceptual gap between tangible particulars and abstract universals. Furthermore, the author extends this framework to explain how phantasia facilitates our psychological processes, particularly in visualizing potential scenarios and outcomes that guide decision making in practical contexts.

The introductory chapter of the book meticulously traces the evolution of images and appearances in Greek literature prior to Aristotle, effectively setting the stage for a nuanced examination of Plato's geometrical methods. These methods prominently featured the use of diagrams as concrete representations of immutable geometrical truths, acting as intermediaries between the perceptible objects and the intelligible forms (Chapter 1). Chapter 2 progresses to argue that the act of geometrical construction, which is pivotal for the formulation of proofs, represents a cognitive activity distinct from both the mere perception of material particulars and the pure intellectual contemplation of unchanging universals. According to the author, Justin Humphreys, this distinctive cognitive function justifies Aristotle's introduction of the imaginative faculty.

In Chapter 3, Humphreys mounts a critical examination of the mainstream interpretation of phantasia as articulated in Aristotle's De Anima III.3, where it is often dismissed as either a peculiar form of perception or simply a retention of perceptual experiences. Building on this critique, Chapter 4 considers a broader array of Aristotelian texts to more robustly support the thesis that Aristotle attributed to phantasia the ability to significantly modify sensory inputs, positioning it as a productive, autonomous and representational power within the psyche.

The central thesis of the book is elaborated in Chapters 5 and 6, where Humphreys explores the instrumental role of phantasia in mathematical thought processes. He argues that the necessity of employing sensible diagrams for illustrating abstract mathematical proofs underscores their imperfect representation of mathematical properties. Phantasia, therefore, is indispensable for the reinterpretation of these diagrams, enabling geometers to transcend the perceptual specifics of the diagrams and make deductive inferences about abstracted mathematical properties. This, Humphreys suggests, is the reason why Aristotle considered geometrical objects as intermediaries between the sensible and the intelligible realms.

The narrative then extends into the practical sphere in Chapters 7 to 9, where Humphreys explores Aristotle's contemplation of the significant role of phantasia in emotional and deliberative processes. The discussion particularly focuses on concepts such as wish (boulēsis), deliberation (bouleusis), shame (aidōs) and other passions, suggesting that phantasia enables individuals to conceptualize practical possibilities that align with their actual circumstances and formulate appropriate life goals.

This perspective posits that Aristotle's conception of phantasia is more akin to our contemporary understanding of productive imagination than is commonly acknowledged. However, I am sceptical of the assertion that Aristotle held such a view. The principal textual support that the book offers for linking phantasia with geometric thought appears in On Memory 449b30–450a5, where Aristotle states, ‘there is no thinking without a phantasm. Indeed the same affection corresponds to thinking and drawing’. However, this appears to merely indicate that, analogous to our need for a visual image like a geometrical figure to construct a proof – despite the image itself not being the proof's subject – we similarly require some form of mental image for cognitive processing. There is no clear implication in this statement that phantasia actively modifies visual perceptions to produce universal mathematical properties for the discursive thought to handle.

Furthermore, an alternative interpretation is that perception alone might suffice to convey the universal concepts with which mathematics engages, albeit cluttered with extraneous details. For instance, in Posterior Analytics II.19, 100a17–b5, Aristotle articulates that ‘though one perceives the particular, perception is of the universal – e.g., of man but not of Callias the man … Thus it is clear that it is necessary for us to become acquainted with the primitives by induction; for perception too instils the universal in this way’. This passage challenges Humphreys's argument that phantasia is essential for bridging the gap between the particular contents of perception and the universal content required for intellectual abstraction. Neither the passage from On Memory nor the related discussion in De Anima III.7 provides sufficient evidence to support the thesis. A more comprehensive analysis of these and related texts would have been beneficial to substantiate the claims made.

Despite these critiques, Humphreys's book stands as a comprehensive examination of the concept of phantasia across both its theoretical and its practical dimensions. While specialists may find some of the arguments and analyses lacking in depth, non-specialists will undoubtedly benefit from the broad overview of the topic that it provides. However, it is important for non-specialist readers to approach with caution, as the main thesis presented is quite controversial and may not be universally accepted within the scholarly community. This work is a notable contribution to the limited but growing body of literature on Aristotelian phantasia, offering valuable insights into its applications across the entire corpus of Aristotle's writings.