the aim of science , he went on to profess , is to define the essential forms , purposes , and modes of development of all species and to arrange them in their natural order in accordance with their complexities of form , the main levels of which , in his view , were the inanimate ( such as rocks and water ) , the vegetative , the animal , and the rational ( i.e. , manwho he saw as the highest order of nature on earth ) .