Aristotle begins by describing the meaning of the words nature and natural. He identifies the meaning of each, and also explains some common phrases which include each of the words. He says all natural things have a principle of motion and of stationariness. He also says that natural things are composed of stone, earth, or a mixture of the two.

According to him, artificial products do not possess the source of their own production. For example, the nature of a bed is of wood. He says that if the bed was planted and began to rot, a shoot may grow from that. Aristotle says that a bed would not be growing, but wood (in the form of a tree), which is the nature of the bed. Another idea of nature is form.

Bones and flesh does not have its own nature, until it is formed in the body. In the second section of this book, Aristotle distinguishes between mathematicians and physicists. He says that they work with similar ideas and materials, but use different methods. He continues to explain how the forms of things can involve motion.

Aristotle explains that nature has two senses: the form, and the matter. He explains that each form has a corresponding special matter. He concludes that the physicist must know the form of essence of matter up to a certain point. The third section explains causes, their character, and number. The whatever a thing comes to be from is the cause.

The form of the thing is also a cause. The source of a change (coming to be or passing away) is a cause. The sake for which an activity is done is a cause. That is an explanation of different senses of cause, and their characteristics. There are a total of six uses for the word cause. In the fourth section, Aristotle tells us that chance and spontaneity are included in cause.

He tells us that physicists shouldn have agreed with the idea that things occur due to chance, but Empedocles speaks of chance in his description of the air and of the parts of animals. Aristotle continues to describe how some people believe that the entire universe was created in a moment of spontaneity. He begins to define what occurrences are due to chance and those that are due to spontaneity. He says that chance cannot be the cause of things that come to be due to necessity. He concludes that chance and intelligent reflection are similar. He ends with the statement that things that come to pass by chance or spontaneity are not caused by necessary or normal reasons, but they do come to pass for the sake of something.

Aristotle begins part six by describing the relationship between spontaneity and chance. He tells us that things that result from chance are from spontaneity, but those from spontaneity are not always due to chance. He explains the three characteristics of things that come to pass due to spontaneity. These occurrences are for the sake of something, do not occur for the end result, and are caused by some external force. He tells us that intelligence and nature both come before chance and spontaneity.

Aristotle then explains that there are four causes, and describes which ones account for matter and which ones account for motion. He also explains how Nature belongs in the class of cause that works for the sake of something. He speaks of necessity through examples of rain and teeth. He explains that these do not occur due to coincidence, but for a reason. Intelligent action also works toward a reason. He uses the example of art to explain how artificial products are made for a reason and so are natural products.

Aristotle tells how mistakes can occur in art and in nature. He mentions that seed must have come before the mature animal. Im not sure where he came out with that (how that ties in). He concludes that nature is a cause that moves toward a certain purpose. Because he spoke of necessity in his description of chance and spontaneity, he takes a moment to explain the concept of necessity. He uses an example of a house.

The purpose of the house is to shelter the occupants. He explains how the foundation and heavier materials must be on the bottom of the structure out of necessity because the lighter materials (wood and such) would not hold the heavier materials. He then uses a mathematical example, which I do not understand.