The Greek Philosopher Aristotle devised a way of classifying animals and plants. He grouped plants and animals into tree: the plants which have vegetative souls, animals with both vegetative and animals souls, and human beings, who have vegetative, animal, and radional souls, as manifested by their reasoning ability and intellectual pursuits. Among organisms, those that could move by themselves ( animals ) and those that could not move by themselves (plants) where grouped separately. Those that could move by themselves were further grouped according to their habitat, whether they were land-dwellers, or air-dwellers.
Those in the second group were classified according to size. In the 16th and 17th centuries, geographical studies led to the discovery of new species of plants and animals. Scholars then classified plants into three groups: trees, shrubs, and herbs.
Aristotle's scheme of classification was not always applicable. Take the case of the sea turtles. They stay underwater to get food, but stay on land to lay their eggs. Are turtles water-dwellers or land-dwellers? Baby frogs or baby toads stay in water.
As they mature, they can live on land. Aristotle's scheme, therefore, did not encompass all organisms.
Aristotle's attempts to classify organisms prompted other scientist to find better ways of classifying organisms. Some worked on determining more reliable ways of looking at how organisms are related to each other.