Parts of Animals Book 1 is mainly concerned with a discussion of the norms (horoi) that govern natural (biological) inquiry. In the present chapter I examine one of those norms, which concerns “how one ought to carry out an investigation of animals” (PA 1.1.639b3–5). Aristotle examines two alternative methods. The first recommends investigating animals species by species (e.g. sparrow, finch, raven). The second begins by grouping species into wider kinds (e.g. bird) and studies those features that belong to them as members of those wider kinds before going on to study those variations that differentiate one form of that kind from another (e.g. variations in beak shape). While scholars have been tempted to conclude that Aristotle rejects the first method outright, I argue that he thinks both approaches are important tools in the biologist’s tool-kit (PA 1.4.644b1–6). In the final section of the chapter I show how this discussion helps bring into focus the broader controversy surrounding the relation between the scientific theory presented in the Posterior Analytics and Aristotle’s scientific practice in the biological works.

As we have seen Physics I identifies matter and form as ‘the causes and principles’ from which naturally generated substances first come into being (e.g. 190b10–23; cf. Metaph. VII 8). On this model, matter plays the role of the subject from which the change proceeds while form is the positive state acquired as a result of the change. When Aristotle returns to the principles of natural generation in GC II 9, he goes to great lengths to show that these two principles alone are not sufficient to account for the change. Instead, we must posit a third principle over and above those two.

In Chapter 2 we raised the question of whether Aristotle thinks that in all cases of coming-to-be (including substantial generation) the subject from which the change proceeds must persist through that change or whether he thinks this holds only for those cases where S comes to be F in the qualified sense. I tried to show that, if Aristotle did think that in cases of substantial generation the pre-existing matter survives to become a constituent of the finished product, it is not obvious that he provides that defence in Physics I as the standard reading assumes. However, because the idea of persistent matter has such a firm hold on the literature, much more will be needed to loosen its grip. Part of the aim of the current chapter is to provide that additional support by examining the account of generation in GC I 1–4.

The seeds of an answer to the question raised at the end of Chapter 7 – how do formal and material natures interact in the creation of a new substantial individual? – have already been sown inChapter 4 in connection with GC II 9. On the reading I defended there, while Aristotle agrees with those more sophisticated materialists who regard natural generation as the effect of the simple bodies and their inherent powers, he ultimately rejects their account on the grounds that the powers they give them are too instrumental (lian organikas) to serve as primary causes of the change (336a1–12). But Aristotle’s positive account in GC II 9 remains undeveloped in two important respects. First, he says very little about the nature of the efficient cause that was ‘vaguely dreamed of’ by all his predecessors but ‘definitely stated’ by none of them (335b7–8).

In the Phaedo (Plato’s) Socrates develops an argument for the immortality of the socto be known as the Law of Opposites (70d6–72a7).

This book is an inquiry into an important yet neglected area of Aristotle’s philosophy: the generation of substances. All change for Aristotle is a form of coming-to-be (or passing-away) in some sense. With some changes the substance already exists and simply becomes qualified in some way, as for example when Socrates (a substance) comes to be healthy from being unhealthy (a change in quality) or comes to be bigger from being smaller (a change in quantity). Aristotle calls this coming-to-be in the qualified sense (gignesthai ti). In cases of substantial generation (what Aristotle calls coming-to-be in the unqualified sense, gignesthai haplôs) the change results in a new substance coming into existence. At the end of development, we say that Socrates has come to be (full stop) rather than saying he has come to be F. This distinction was not universally accepted by Aristotle’s predecessors.

I now want to turn to the generation of biological substances in the Generation of Animals. I have stressed the fact that Aristotle treats living things as substances ‘most of all’ (Metaph. 1034a3–4) and so biological generation should be seen as substantial generation par excellence. This forms the focus of the next two chapters. The central aim of the discussion is to set out in detail what I shall call Aristotle’s “reproductive hylomorphism”, which is a more specific application of the basic hylomorphic model from the foundational works to the generation of living things. By way of introduction I shall begin with some remarks about the project of the GA itself.

In the previous chapter I argued that in the context of GA I Aristotle uses the hylomorphic model primarily as a way to analyse the causal contributions of male and female seed to the formation of the primitive embryo (embryogenesis). In this context semen is said to give form to the menstrual blood only in the purely mechanical sense of imposing a determinate limit or boundary on her indeterminate fluid. In GA II 4–5 Aristotle uses the hylomorphic analysis as a way to identify the parents’ reproductive contributions to the substance that comes to be from the embryo (the completed offspring). He presents his account in two stages. In GA II 4 he argues that the father provides the offspring’s form in the sense of its soul while the mother provides the body that underlies the soul as its subject. He then refines this account in GA II 5 by identifying the father’s exclusive contribution with sensory soul.

In Chapters 5 and 6 we saw that Aristotle treats male and female as ‘principles’ (archai) of generation both in the sense of starting points (animals come to be from the union of male and female) and in the sense of causes (the male as the efficient cause, the female as supplying the material cause). However, Aristotle does not treat male and female as causally basic principles in the sense of being causes of other things while nothing more fundamental is the cause of them (cf. GA 788a14–16). At the beginning of GA II 1 Aristotle tells us that the existence of males and females themselves can be traced to a higher principle (731b24–5: anôthen) namely, the divine. And so, they are not the most basic principles of animal generation since something more fundamental is the cause of them.

At the outset of the Physics Aristotle tells us that when the objects of any inquiry have ‘principles, causes, or elements’, knowledge and understanding are acquired by grasping these: ‘For we do not think we know a thing until we are familiar with its primary causes or first principles and have carried out our analysis as far as its elements. Clearly, then, also in the science of nature our first task will be to determine its principles’ (184a10–16). The aim of the next three chapters is to present Aristotle’s general model of substantial generation by examining those principles from which natural substances first come into being. Each of the three chapters focuses on a different set of texts. This chapter explores the basic hylomorphic model of coming-to-be from the perspective of Physics I, with an emphasis on the account in Physics I 7 (which is generally taken to be the locus classicus of that model).

As we have seen, Aristotle opens the Generation of Animals by announcing that he has already dealt with three of the four causes of animals and their parts (formal, final, and material) and that it remains to discuss the efficient cause. For ‘to inquire into this and to inquire into the manner of generation for each thing is, in a way, the same thing’ (GA I 1, 715a1–18). But here we immediately encounter a puzzle. On the one hand, the GA routinely identifies the male principle as the primary efficient cause of the animal and its parts, which is housed in another individual of the same species, namely the father. This would suggest that generation has an external efficient cause (external to the thing that comes to be from it).