Few people have influenced contemporary philosophy of mind as profoundly as the late Hilary Putnam. One of his best known contributions was the formulation of functionalism. As he understood it, functionalism claims that mental states are functional states—postulates of abstract descriptions, like those employed in computer science, which ignore a system’s physical details and focus instead on the ways it correlates inputs with outputs. Psychological descriptions in particular focus on the ways a system correlates sensory inputs with behavioral outputs, and mental states are the internal states that correlate the two.

By the mid-1970s functionalism had become the dominant outlook in philosophy of mind. But Putnam, showing his characteristic independence of mind, became dissatisfied with the view. He did not retreat to substance dualism or idealism. He was convinced that we are physical beings whose capacities are essentially embodied in the physical mechanisms that compose us, yet he was also a committed antireductionist. He denied that physics, chemistry, and neuroscience could yield an exhaustive account of what we are and what we can do. In articulating a pro-physical yet anti-reductive view along these lines, Putnam found inspiration in a new source: Aristotle.

Aristotle’s ideas had been dismissed in many quarters of the philosophical world as expressions of a bygone pre-scientific age. But Putnam saw through the dismissive haze to the empirically and philosophically-respectable core of Aristotle’s philosophy, ‘hylomorphism’.

Hylomorphism claims that form or structure is a basic ontological and explanatory principle. Some individuals, paradigmatically living things, consist of materials that are structured or organized in various ways. You and I are not mere quantities of physical materials; we are quantities of physical materials with a certain organization or structure. That structure is responsible for us being and persisting as humans, and it is responsible for us having the particular developmental, metabolic, reproductive, perceptive, and cognitive capacities we have. The hylomorphic notion of structure is very close to the notion of natural organization that many biologists appeal to – something amply illustrated by biology textbooks which claim that biological organization is responsible for the unity and persistence of organisms through the influx and efflux of matter and energy that characterize their interactions with the wider world.

In the mid-80s Putnam and Martha Nussbaum co-authored a paper that fueled interest in hylomorphism among philosophers of mind. The idea that a hylomorphic notion of organization or structure might provide resources for solving mind-body problems was not new. Decades earlier, John Dewey (another of Putnam’s inspirations) suggested that the key to solving mind-body problems was to reject the basic assumptions that motivated them – assumptions that had been enshrined by Descartes and others during the Scientific Revolution. He proposed replacing those assumptions with new ones based on an empirically-warranted notion of structure like the hylomorphic one. If thought, feeling, perception, and other mental phenomena were species of structural phenomena, Dewey reasoned, and structure was uncontroversially part of the natural world, then there could be no real problems finding a place for mind in the natural world – there could be no real mind-body problems.

From a hylomorphic perspective, mind-body problems arise only for a worldview that rejects hylomorphic structure. Structure carves out distinctive individuals from the otherwise undifferentiated sea of matter and energy described by our best physics, and it confers on those individuals distinctive powers. If hylomorphic structure exists, the physical universe is punctuated with pockets of organized change and stability—composite physical objects (paradigmatically living things) whose structures confer on them powers that distinguish what they can do from what unstructured materials can do. Those powers include the powers to think, feel, and perceive. A worldview that rejects hylomorphic structure, by contrast, lacks a basic principle to distinguish the parts of the physical universe that can think, feel, and perceive from those that can’t, and without a basic principle that carves out zones with distinctive powers, the existence of those powers in the natural world can start to look inexplicable and mysterious. If there is nothing built into the basic fabric of the universe that explains why Zone A has powers that Zone B lacks—if nothing explains why you, say, have the power to think, feel, and perceive, while the materials surrounding you do not, then the options for understanding the existence of those powers in the natural world become constrained: either they must be identified with the powers of physical materials taken by themselves or in combination (as panpsychists and many physicalists claim), or their existence must be taken as an inexplicable matter of fact (as many emergentists and epiphenomenalists claim), or their existence in the natural world must be denied altogether (as substance dualists and eliminative physicalists claim). If there is hylomorphic structure, however, the options are no longer constrained in this way. Distinctive powers like yours and mine exist in the natural world because structure exists in the natural world.

It would take several decades for Putnam’s retrieval of Aristotelian ideas to become more than a mere suggestion. One reason was sociological: philosophers of mind and philosophers who took the merits of hylomorphism seriously (mostly scholars of ancient and medieval philosophy) had different professional concerns and operated in different scholarly spheres – something that inhibited fruitful collaboration between them. Another reason was philosophical: the assumptions motivating mind-body problems turned out to be deeper and more pervasive than philosophers like Dewey had imagined. It took a revival of Aristotelian ideas in metaphysics in the late 90s and early 2000s to unearth them. That revival, which was evident especially in neo-Aristotelian accounts of powers and composition, provided the conceptual resources needed to formulate hylomorphism in a way that could contribute to live debates in the philosophy of mind.

The number of philosophers working on hylomorphism and its implications for philosophy of mind continues to grow. Time will tell if Putnam’s instincts were right, and a hylomorphic framework really does provide resources for solving mind-body problems. It may not be his best-advertised contribution to the philosophy of mind, but it may end up being his most important.

Featured image credit: Vitreous metaphysics II, by Alkan Chipperfield. CC-BY-SA-2.0 via Flickr.