Before developing a hierarchy we need to finalise the elements which will define the basis for classification.

Based on these , the common characteristics are used for forming sub-groups.

For example, plants differ from animals in their body design, process of food formation i.e. photosynthesis, etc. But, the main classification between plants & animals is based on the property of locomotion because plants cannot move but animals can. Hence, locomotion is considered as the fundamental characteristic for distinguishing between plants and animals.