More Leroi

The problem is that here. as so often. Aristotle's technical vocabulary is underdetermined He's very reluctant to coin new terms even When he badly needs them. He's not entirely oblivious to the problem, He’ll often say that a given term is used in several different senses, and even tell us what they are but then. as often as not, leaves us guessing which one he means. 

Indeed. there’s a third sense in which Aristotle uses tides. It’s related to the other two. but goes much deeper, and is much more surprising It's the appearance of an organism, but if this is not too paradoxical its appearance when it cannot yet be seen. It is the ‘information’ or the formula’ which was transmitted to it by its parents, from which it built itself in the egg or womb, and which it will, in turn, transmit to its progeny It is in this sense that Aristotle thinks that the nature of a thing resides primarily in its form. 

To speak of eidos as ‘information’ risks anachronism. Aristotle certainly does not conceive of information in the general sense that we do. Yet this interpretation is supported by passages in which he draws a parallel between the transmission of animal form and the transmission of knowledge. In The Parts of Animals Aristotle considers how a woodcarver might explain his art. He clearly wouldn’t just talk about the wood that’s merely the matter out of which it’s built. Nor would he just talk about his axe and auger -they’re merely tools, Nor would he just talk about the strokes that he makes -that’s mere technique. No, if he is really to convey the origin of the thing he's making, he has to talk about the idea that he had when he began his work the process by which it will unfold in his hands, its final design and ultimate purpose he must talk about its eidos. In the same way, when a scientist seeks to explain why living things have the features they do, he must talk about their aide. It’s just that the forms of living things are not. Plato held, located in the mind of some divine craftsman, but rather located in their patents' seeds. 

There's a passage in the Metaphysics where Aristotle gives another metaphor for the relationship between material and formal natures. Rather marvellously, he compares the components of a body to a symbolic system. Some things he says. are compounds. The syllable ab is a compound of the letters a and b, But putting a and b together is not enough to give you that particular syllable; you need something else: you need to specify the order of the letters (lest you get ba instead) or, as we would now say, you need information. In the same way, flesh is a compound of Fire and earth and something else: the way in which they are ordered. And that order is the form and nature of flesh. 

Aristotle's belief that we should attend less to the matter than to the 
informational structure of living things makes him seem like a molecular geneticist avant la lettre. He did not somehow miraculously anticipate the discovery of DNA: it’s mere coincidence that he used an ordered alphabetical sequence ab v. ba to describe forms as we describe nucleotides. Yet, in retrieving forms from the Platonic realm-beyond-the-senses, Aristotle answered, and answered correctly, the question: what is the immediate source of the design that we see in living things? It is the information that they inherit from their parents.

and

Aristotle distinguishes the rules for debating opinions from the rules for constructing scientific explanations. The first he called ‘dialectic’, the latter ‘demonstration‘ (the Greek is apodeixis). By ‘demonstration' he mean“ exactly what a modem scientist means when he says, ‘we have demonstrated that A is the cause of B’ -that is, he and his collaborators have shown that the presence of A is a necessary and sufficient condition for B. He had a high notion of the power of scientific demonstrations: he thought that they delivered truth. That’s because they are the products of logical operations. Aristotle invented the theory of inferential logic known as his syllogistic. It was his greatest technical achievement and dominated the subject for millennia even if it was incomplete and, in parts, wrong. His syllogistic aimed to deduce new conclusions from established premises where the premises are propositions that contain a subject and a predicate. e.g. ‘All octopuses [subject] are eight legged [predicate].’ To analyse such statements he invented a formalism that substituted letters for the terms, e.g. ‘All A are B.’ This formalism allowed him to speak generally of all propositions of a given form, manipulate them and derive the many results that he did. 

For Aristotle, a scientific demonstration rests upon a syllogism. But to qualify as a demonstration a syllogism must meet certain conditions. First, the premises of the syllogism must obviously be true. Second, the premises of the syllogism must be more immediate, more empirically apparent, than its conclusion (at least in natural science as distinct from geometry). Third, it must concern universals rather than particulars. In fact, Aristotle thinks that it’s impossible to have scientific knowledge of individuals. To say that this octopus has eight legs gets us nowhere; scientific knowledge can only 
begin once we‘ve established that all octopuses have eight legs or at least that all normal octopuses do. Finally only universal, assertive and assertoric propositions can form the basis of demonstrations: ‘All A are B; all B are C; therefore all A are C.’ Logicians refer to such syllogisms as being in the 'mood' of‘Barbara’. Such logical strictures may seem remote from the modern scientific 

method and so, in a way, they are. But Aristotle’s reason for grounding scientific knowledge in his syllogistic is, I believe, one familiar to any modern scientist. I suggested that, far from being a natural history or a taxonomy, Historia animalum is a search for associations among the traits that animals possess; that it is, in fact, a data trawl. His syllogistic, then, provides a powerful way of securing those associations of showing that they are true. Secure associations, in turn, demand causal explanations which his syllogistic also identifies. 

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I have been speaking of Aristotle’s ‘theory of demonstration’ as if there is just one of them. In the Posterior Analytics he certainly devote; most space to the method I have sketched. But he also allows that there are other modes of demonstration though he’s quite vague about how they work. In The Parts of Animals he says that the methods of demonstration in natural science are actually different from those in ‘theoretical sciences’ such as geometry. In biology, he suggests that we should start with the end the teleological purpose of an animal and work our way deductively back to infer how the animal’s various parts serve that purpose. Such demonstrations can also, with some twisting, be couched in syllogistic terms. 

Although demonstration is the beating heart of his scientific method Aristotle acknowledges that science rests on various indemonstrable statements. These include the axioms of his syllogistic as well as various Primary definitions. For example, geometry requires a definition of‘spatial magnitude and arithmetic a definition of ‘unit'. The axioms and primary definitions of biology are less obvious but include statements such as ‘nature does nothing in vain‘ an apophthegm that he puts to hard use. Aristotle isn’t clear how such ideas can be justified, and suggests that their truth is just apparent by induction (epagoge), but argues nonetheless that they're needed if science is to get off the ground. 

This is certainly right. In our day there are people who think, all evidence to the contrary, that science is just one system of beliefs among many. Aristotle had to contend with them too. Some people, he says, claim that scientific knowledge is impossible because any inference we make must rely on some previous inference, and that must rely on another, and so on to infinity so that, ultimately, we can know nothing. Other people. he continues, claim that anything can be demonstrated: everything is true hence nothing is true. 

Aristotle recognizes that both thoughts are lethal to the possibility of science, and he deals with them briskly. No, there isn’t an infinite regress of inferences, nor is it true that everything can be demonstrated. because our arguments ultimately begin with axioms and our perception of the empirical world. His language is combative. It has to be. He has to show against his opponents, not just Plato but the sophists with their razorsharp dialectic, that it is possible to extract real knowledge from the sensible world. We may wonder whether he succeeded. Modem science rests on fundamental axioms no less than Aristotelian science. and scientists mostly justify them by the fact that they work. But Aristotle could hardly defend his assumptions, as a modern scientist can, by flicking on a light.‘