It identifies 'what makes of what is made and what causes change of what is changed' and so suggests all sorts of agents, non-living or living, acting as the sources of change or movement or rest
In the case of two dominoes, when the first is knocked over it causes the second also to fall over
In the case of animals, this agency is a combination of how it develops from the egg, and how its body functions
The final cause (telos) is its purpose, the reason why a thing exists or is done, including both purposeful and instrumental actions and activities
The final cause is the purpose or function that something is supposed to serve
This covers modern ideas of motivating causes, such as volition
In the case of living things, it implies adaptation to a particular way of life
Optics 

Aristotle describes experiments in optics using a camera obscura in Problems, book 15
The apparatus consisted of a dark chamber with a small aperture that let light in
With it, he saw that whatever shape he made the hole, the sun's image always remained circular
He also noted that increasing the distance between the aperture and the image surface magnified the image
Chance and spontaneity 

According to Aristotle, spontaneity and chance are causes of some things, distinguishable from other types of cause such as simple necessity
Chance as an incidental cause lies in the realm of accidental things, "from what is spontaneous"
There is also more a specific kind of chance, which Aristotle names "luck", that only applies to people's moral choices
the sun shines on all the stars and the earth screens none of them." He also wrote descriptions of comets, including the Great Comet of 371 BC
Geology and natural sciences 

Aristotle was one of the first people to record any geological observations
He stated that geological change was too slow to be observed in one person's lifetime
He spent two years observing and describing the zoology of Lesbos and the surrounding seas, including in particular the Pyrrha lagoon in the centre of Lesbos
His apparent emphasis on animals rather than plants is a historical accident: his works on botany have been lost, but two books on plants by his pupil Theophrastus have survived
Aristotle reports on the sea-life visible from observation on Lesbos and the catches of fishermen
He describes the catfish, electric ray, and frogfish in detail, as well as cephalopods such as the octopus and paper nautilus
His description of the hectocotyl arm of cephalopods, used in sexual reproduction, was widely disbelieved until the 19th century
He gives accurate descriptions of the four-chambered fore-stomachs of ruminants, and of the ovoviviparous embryological development of the hound shark
Darwin, too, noted these sorts of differences between similar kinds of animal, but unlike Aristotle used the data to come to the theory of evolution
Aristotle's writings can seem to modern readers close to implying evolution, but while Aristotle was aware that new mutations or hybridizations could occur, he saw these as rare accidents
For Aristotle, accidents, like heat waves in winter, must be considered distinct from natural causes
He was thus critical of Empedocles's materialist theory of a "survival of the fittest" origin of living things and their organs, and ridiculed the idea that accidents could lead to orderly results
To put his views into modern terms, he nowhere says that different species can have a common ancestor, or that one kind can change into another, or that kinds can become extinct
Scientific style 

Aristotle did not do experiments in the modern sense
He used the ancient Greek term pepeiramenoi to mean observations, or at most investigative procedures like dissection
In Generation of Animals, he finds a fertilized hen's egg of a suitable stage and opens it to see the embryo's heart beating inside
Instead, he practiced a different style of science: systematically gathering data, discovering patterns common to whole groups of animals, and inferring possible causal explanations from these
This style is common in modern biology when large amounts of data become available in a new field, such as genomics
It does not result in the same certainty as experimental science, but it sets out testable hypotheses and constructs a narrative explanation of what is observed
In this sense, Aristotle's biology is scientific
From the data he collected and documented, Aristotle inferred quite a number of rules relating the life-history features of the live-bearing tetrapods (terrestrial placental mammals) that he studied
Among these correct predictions are the following
Brood size decreases with (adult) body mass, so that an elephant has fewer young (usually just one) per brood than a mouse
Lifespan increases with gestation period, and also with body mass, so that elephants live longer than mice, have a longer period of gestation, and are heavier
As a final example, fecundity decreases with lifespan, so long-lived kinds like elephants have fewer young in total than short-lived kinds like mice
Animals came above plants, and these in turn were above minerals
He grouped what the modern zoologist would call vertebrates as the hotter "animals with blood", and below them the colder invertebrates as "animals without blood"
Those with blood were divided into the live-bearing (mammals), and the egg-laying (birds, reptiles, fish)
Those without blood were insects, crustacea (non-shelled – cephalopods, and shelled) and the hard-shelled molluscs (bivalves and gastropods)
He recognised that animals did not exactly fit into a linear scale, and noted various exceptions, such as that sharks had a placenta like the tetrapods
To a modern biologist, the explanation, not available to Aristotle, is convergent evolution
Philosophers of science have generally concluded that Aristotle was not interested in taxonomy, but zoologists who studied this question in the early 21st century think otherwise
He believed that purposive final causes guided all natural processes; this teleological view justified his observed data as an expression of formal design
Psychology

Soul 

Aristotle's psychology, given in his treatise On the Soul (peri psychēs), posits three kinds of soul ("psyches"): the vegetative soul, the sensitive soul, and the rational soul
The human soul incorporates the powers of the other kinds: Like the vegetative soul it can grow and nourish itself; like the sensitive soul it can experience sensations and move locally