Aristotle's "Four Causes"
Aristotle sought to explain the World as logical, as a result of causes and purposes, The "Four Causes" are his answers to the question Why: "We do not have knowledge of a thing until we have grasped its why, that is to say, its cause." "Cause" is the traditional translation of the Greek aitia (αἰτία), which has a technical sense better translated as "explanation".
Aristotle argued that there are four kinds of answers to "Why" questions (Physics II:3, and Metaphysics V:2). Cause results in change.
Matter: a material cause is determined by the matter that composes the changing things. For a table, that matter might be wood; for a statue, it might be bronze or marble.
Form: a formal cause is due to the arrangement, shape, or appearance of the thing changing. Numerical relationships are of this nature: I and II form III.
Agency or Efficiency: an efficient cause consists of things apart from the thing being changed, which interact so as to be an agency of the change. For example, the efficient cause of a table is a carpenter acting on wood. In the natural world, the efficient cause of a child is a father.
End or Purpose: a final cause is that for the sake of which a thing is changing. A seed's end is an adult plant. A sailboat's purpose is sailing. A ball at the top of a ramp will finally come to rest at the bottom.
For example: the cause or explanation of a table is that it is solid and grained because it is made of wood (material), it does not collapse because of its design with four legs of equal length (formal), it occurs as it does because a carpenter made it from wood (agency, or efficiency), and it has particular dimensions because of is intended to support objects (purpose).
In English, the addition of the suffix "-al" turns a noun into an adjective. For example, the tropics are tropical. In Aristotelian Greek, the two forms are both nouns. To understand Aristotle's system, look for the original noun. Thus, "ideal" means "pertaining to ideas" rather than "perfect", "material" means "pertaining to matter" rather than "stuff", "formal" means "pertaining to form" rather than "proper", and "final" means "pertaining to ends" rather than the end itself.
Causes account for both artificial (constructed) and natural (living) things. In modern Biology, we understand "natural" as "pertaining to nature" rather than "non-artificial". Thus "Natural Selection" is differential survival & reproduction as it occurs in Nature, in contrast to "Artificial Selection", for example by pigeon breeders. Natural Selection can be understand as an efficient cause, by which organic evolution occurs. Both worldviews use similar vocabularies, with contrasted implications. Especially in evolutionary biology, we avoid explanations of phenomena expressed in terms of end results or purposefulness. The habit can be a hard one to break.
For example: a textbook statement such as "Reptiles have dermal scales in order to prevent desiccation on land" tacitly assumes a formal cause, that Nature arranges things functionally, and a final cause, that scales exist for osmoregulation. In fact, we know as matters of historical fact that the evolution of scales long preceded the origin of terrestrial animal life, that modern amphibian classes lost their ancestral scales (which assists in dermal respiration), and that reptilian scales are of multiple origin and function.
