<i>The Powers of Aristotle's Soul</i>

Johansen seeks in The Powers of Aristotle's Soul to establish Aristotle as the progenitor of faculty psychology, “the attempt to account for a multitude of psychological phenomena by reference to a few permanent or inborn psychological capacities” (1). Johansen draws support for this thesis from a comprehensive interpretation of Aristotle's treatise on the soul, De Anima (DA). According to Johansen, Aristotle endeavors in DA to explain the full range of life activities of organisms as diverse as plants, animals, and humans by reference to three basic psychological capacities: nutrition, perception, and intellect. The results of this approach are impressive: Johansen delivers an attractive interpretation of DA not only as systematic and internally unified but as continuous with Aristotle's natural philosophy as a whole. His detailed and incisive discussion will be of interest both to scholars of DA, who will find much to grapple with in these pages, and to historians and philosophers concerned with Aristotle's place in the development of psychology and the life sciences.The first three chapters set out the framework for Johansen's “naturalistic” interpretation. Johansen argues that DA occupies a foundational place in Aristotle's biology: in seeking “to gain knowledge of the soul by defining its essence” (9), DA seeks to identify the principles that explain the features belonging to living beings qua ensouled. Employing the Posterior Analytics model of scientific explanation, Aristotle aims to set out the essential features of soul that provide the premises from which the necessary activities of living beings may be demonstrated (chapter 2). However, the focus of the discussion shifts to the capacities of soul when Aristotle concludes that there is no essence-giving account of soul over and above accounts of soul as the cause of particular sorts of life. Johansen's interpretation stresses the continuity of Aristotle's capacity-centered approach with DA's explanatory project: the basic capacities Aristotle describes as “parts” of soul, and whose essence he seeks to define in the remainder of DA, are parts of the definitions of various types of soul, differentiae that mark off one type of soul from the rest (chapter 3).Johansen then turns to the status of psychological capacities as causes of life activities. On the basis of Aristotle's discussions of capacity (dunamis) and activity (energeia) in Metaphysics Θ and elsewhere, he provides a detailed account of the causal role of psychological capacities in bringing about natural changes in the body, such as those involved in nutrition and perception (chapter 4). A novel feature of this account is the causal role of the objects of psychological capacities, which Johansen takes to be definitionally prior because they are the formal cause of natural changes. So although the soul is the final cause of nutrition or perception to the extent that the body is functionally organized for the actualization of these capacities, it is the object of nutrition or perception that determines what kind of change it is (chapter 5).1Here as elsewhere Aristotle treats nutrition as an explanatory paradigm. The nutritive capacity itself serves as the efficient cause of this transformation (chapter 6).Johansen argues that all of the capacities of soul are likewise efficient causes of the changes they enable. Perception, for instance, is a passive capacity in which the animal is somehow affected by a perceptible object. Nevertheless, Johansen argues that the soul has an efficient-causal role here too, and this in two ways: first, the nutritive soul operating in utero brings the perceptual soul into first actuality; and second, the perceptual soul in a state of second potentiality is in a way already perceiving. On this view, the efficient-causal role of the perceptible object is to cause the activated sense to perceive a determinate perceptible quality (chapter 7).Finally, for Johansen the body is the material cause of these psychological activities because it is hypothetically necessary for the exercise of the relevant capacities; so conceived, the formal account of psychological changes carries no implications for the sort of change (if any) occurring at the level of matter. Thus, for instance, any material change involved in vision, which is formally characterized as the assimilation of the sense to the perceived object qua colored, needn't consist in the literal coloring of the eye (chapter 8).The interpretation that emerges portrays the various types of soul as composed of a set of basic psychological capacities that are discrete and modular in the sense that they enjoy definitional independence and operate relative to distinct domains (277). In the chapters that follow, Johansen shows how Aristotle's framework accommodates “derivative” capacities such as phantasia and desire, which are defined by reference to, and so “depend” on, one or more basic capacities. Johansen takes Aristotle's treatment of these capacities to reflect his commitment to explaining the myriad activities that living beings engage in qua ensouled in terms of the operation of a minimal set of basic psychological capacities. Thus, Aristotle attributes such extended perceptual activities as common, incidental, and higher-order perception to the operation of the five special senses (chapter 9), and such quasi-perceptual activities as memory and dreaming to the operation of phantasia, which Aristotle takes to belong to the perceptual capacity (chapter 10).Another notable case is locomotion, a capacity that Aristotle takes to be both derivative—it is definitionally dependent on desire, which Aristotle attributes to the perceptual capacity—and distinctive of a special class of roaming animals (chapter 12). Locomotion thus appears to pose a problem for Johansen's interpretation of the parts of soul as corresponding to the differentiae that mark off the various types of soul. Johansen responds to this worry by pointing out that locomotion can differentiate a subclass of animals because Aristotle's analysis makes reference to capacities that are not possessed by all animals; in particular, the sort of desire capable of moving an animal requires phantasia, which Aristotle denies to some animals (251).However, this response does not seem to appreciate the depth of the worry. For Johansen, a part of soul is a part of a definition of soul, an element of the definition of a type of soul that distinguishes it from the definition of other types of soul. Yet, although the locomotive capacity distinguishes a distinctive type of soul, Aristotle does not consider it to be a part of soul. It would seem to follow that, however Aristotle construes psychic parthood, it cannot be more than a necessary condition that a part of soul be a part of a definition of soul.The closing chapters of The Powers of Aristotle's Soul are the most interesting for Johansen's thesis that DA is an exercise in faculty psychology. Having already stressed the limits of DA's naturalistic perspective in the discussion of intellect, which unlike other psychological capacities does not have material changes directly involved in its exercise (chapter 11), Johansen turns in the penultimate chapter (chapter 13) to another limitation of Aristotle's approach, one concerning DA's relation to the psychological treatises that compose Parva Naturalia (PN). Johansen argues that Aristotle's transition in PN to the activities common to body and soul marks a turn to aspects of psychological capacities and their objects that are not mentioned in the definition of the types of soul but follow from the essence of soul. The project of PN therefore highlights the explanatory priority of the definition of soul to the rest of Aristotle's biology.The final chapter (chapter 14) considers the modularity of the basic psychological capacities from the “holistic” perspective that Aristotle adopts to explain their contribution to the good of the organisms that possess them. From this perspective, Johansen argues, we observe that the way a given capacity is actualized may differ according to the “psychological hierarchy” in which it is embedded, as the way nutrition is actualized will differ between plants and animals. We also see that one capacity may be integrated with another in its hierarchy in a way that affects its “internal” properties, as (on Johansen's view) the integration of the perceptual with the intellectual capacity enhances the content available to perception.Lastly, from the holistic perspective of the compound organism, we see that how a capacity is actualized may be affected by features of the organism's matter (though not in a way that threatens the explanatory priority of the formal and final cause). These holistic phenomena do not, however, undermine the modularity of the basic capacities of soul. To the contrary, it is the definitional independence of these capacities that allows us to view these phenomena as complex operations of a minimal set of basic psychological capacities.In sum, Johansen presents an admirable defense of the thesis that Aristotle aims in DA to attribute the full range of psychological phenomena to the operation of a minimal set of basic capacities. And though, as I suggested, certain elements of Aristotle's theory, and in particular his notion of psychic parthood, require closer scrutiny, Johansen's take on DA is on the whole illuminating.

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