He died there the following year. The early writings of Aristotle were intended for the general public, some written in dialogue form, with a largely Platonic outlook. They are basically lecture notes which have been edited several times over several generations, which makes the chronology of his writings very complicated. Substance is prior to the other categories since substances exist as separate entities, while the other categories exist only as the qualities of substance. For a dog is an animal, a dog is not just some quality of an animal.
Form is different from matter.
A chair's form is the structure of the chair, the chair's matter is wood. The chair's matter, wood, can also be divided into form and matter, since wood is made of earth, air, water, and fire combined in a particular way. He raises the question whether form can have no matter, to which he answers that this form without matter is God. If matter becomes a chair the matter is chair potentially, or capable of being a chair, whereas the form is the actuality in virtue of which it is now an actual chair. The causes apply to things and not events.