Avicenna's Ontology and the Unity of Biological Theories: A Reconsideration — Epoche C2
Research note: reconsidering scientific unity in biology through Avicenna's ontology The question is whether the theories of biology are unified in the way the theories of physics are said to be, and the proposal tested here is that two doctrines of Ibn Sīnā — known in the Latin West as Avicenna — describe what biological unity consists in better than the formal and pragmatic accounts developed for physics. The first doctrine concerns what makes a science one science; the second concerns what makes a living thing one thing. They give different answers about biology, and the difference is the substance of this note. I should say at the outset that the answers are not the ones I expected when I began, and that on one of the two the doctrine tells against the position I had hoped it would support. The current dispute needs setting out first, because "unity" is used for at least two incompatible things and the disagreement is real rather than terminological. On one side stands the unificationist account of explanation, given its most developed form by Philip Kitcher in 1989: to explain is to derive, and the explanatory store of a body of knowledge is the set of argument patterns that yields the greatest number of conclusions from the fewest and most stringent patterns. On this view unification is not a byproduct of explanation but its currency, and the more unified a body of theory is, the more it explains. On the other side stands Margaret Morrison, whose Unifying Scientific Theories of 2000 argues that the two come apart. Her cases are the central unifications of physics — Maxwell's electrodynamics, and the electroweak theory — and her finding is that what does the unifying is typically a mathematical structure, a gauge symmetry or a formal analogy, which carries no account of the physical mechanism behind the phenomena it brings together. Unification is achieved; explanation is not thereby delivered. The compressed version of this note credited Morrison with exploring the interplay of physical concepts and mathematical structures, which understates her considerably: her thesis is a separation thesis, and it supports rather than opposes the line of argument pursued here. The question: can the unity within biological theories be understood primarily through formal coherence or pragmatic success, in the way the unity sought in physics is understood? The prevailing answer looks to reduction: complex biological phenomena are to be explained by chemical and ultimately physical interactions, and the unity of biology is then inherited from the unity of what it reduces to. The programme has been enormously productive and nothing here disputes its yield. What it has not delivered is an account of the organisational levels at which biological explanation actually proceeds. Ernst Mayr's formulation of 1961 remains the cleanest statement of the problem from inside the discipline. Biology asks two kinds of question about any trait, and they take two kinds of answer: proximate questions, about the physiological and developmental machinery that produces the trait in an individual, and ultimate questions, about the evolutionary history that made the trait prevalent in a population. A complete proximate answer does not answer an ultimate question, and vice versa. Mayr's point is not that molecular explanation fails; it is that supplying it leaves a second explanatory demand entirely unmet, which is not the situation a successful reduction produces. The counter-argument: biological theories, with their organisational levels and their two irreducible explanatory registers, resist purely formal or pragmatic unification. Their unity, if they have one, must lie elsewhere. Avicenna's first doctrine: a science is one through its subject The first Avicennan resource is a criterion for the individuation of sciences, set out in the opening treatise of the Ilāhiyyāt , the metaphysics of his encyclopaedia Kitāb al-Shifāʾ (The Book of Healing). Every demonstrative science, Avicenna holds, has a subject matter — a mawḍūʿ — whose existence it does not establish but presupposes, and whose essential accidents, the attributes belonging to it precisely as the thing it is, are what its demonstrations concern. A science is one science in virtue of the unity of that subject. The criterion is not decorative; Avicenna applies it to metaphysics itself and derives a substantive result. God cannot be the subject of metaphysics, because a science never demonstrates the existence of its own subject, whereas demonstrating that a necessary existent exists is exactly what metaphysics undertakes. The subject must therefore be the existent as such, with God sought within the science rather than presupposed by it. Transposed to our question, the criterion changes what is being asked. "Is biology unified?" becomes: does biology have a single subject whose essential accidents its demonstrations concern? And that reframing exposes a category difference that the physics comparison has been obscuring. The formal accounts ask whether a set of theories shares a mathematical structure. The Avicennan question asks whether a set of objects shares a nature. These can come apart in both directions, and routinely do. A shared formalism over heterogeneous subjects is commonplace — mean-field methods serve statistical mechanics and network epidemiology alike, and nobody concludes that magnets and epidemics form one subject matter. A shared subject investigated through heterogeneous formalisms is equally common, and it is arguably the situation in the study of any single organism. Here, however, the doctrine yields a result I did not want. Avicenna's criterion is demanding: the subject must be such that the science's demonstrations proceed from its essential accidents. Suppose we propose "the living thing" as biology's subject. Its essential accidents, in the Aristotelian inventory Avicenna inherits, would be nutrition, growth, reproduction, perception and