  Unlike Descartes' purely extended matter, which can exist on its own having only size and shape, many scholastic Aristotelians held that prime matter cannot exist on its own. To form a substance, or something that can exist by itself, prime matter must be “informed” by a substantial form (a form that renders something into a substance). The four Aristotelian elements, earth, air, fire, and water, had substantial forms that combined the basic qualities of hot, cold, wet, and dry: earth is cold and dry; air is hot and wet; fire is hot and dry; and water is cold and wet. These elements can themselves then serve as “matter” to higher substantial forms, such as the form of a mineral, or a magnet, or a living thing. Whether in the case of earth or of a living rabbit, the “form” of a thing directs its characteristic activity. For earth, that activity is to approach the center to the universe; water has the same tendency, but not as strongly. For this reason, Aristotelians explained, the planet earth has formed at the center, with water on its surface. A new rabbit is formed when a male rabbit contributes, through its seed-matter, the “form” of rabbithood to the seed-matter of the female rabbit. This form then organizes that matter into the shape of a rabbit, including organizing and directing the activity of its various organs and physiological processes. The newborn rabbit's behavior is then guided by its rabbit-specific “sensitive soul,” which is the name for the substantial form of the rabbit. Other properties of the rabbit, such as the whiteness of its fur, are explained by the “real quality” of white inhering in each strand of hair.