The most familiar order is the classificatory order. Here things are recognised as belonging to one category and are assigned names.
We assign names such as ‘dog’, ‘cat’, ‘milk’, ‘tree’ etc. to individual things and make each of them a distinct class.
A layman also classifies things, animals or events into classes. In the most primitive stage of man’s history things, events or animals have been classified on the ground of
Natural similarity. On the basis of natural resemblance the dogs make a class as the members resemble one another on important points, and differ from other classes. Dogs are different from cats as cats make a class on the basis of inherent resemblances. This classification is done mostly from a practical point of view.
But in science the classificatory order is introduced on the basis of structural similarity. On the ground of certain characteristic resemblances classification is made. Cats, dogs, cows, whales are classified as mammals; iron, copper, lead, mercury are classed as metals; and iron, oxygen, gold…. are classed as elements on some deep seated points of similarity.
A structural similarity is connected with some important properties. Thus scientific classification helps to know the important or structural points of resemblances among the members and the invariable properties associated with them.
Classification of man on the basis of caste, religion, nationality etc. is an artificial or superficial classification whereas classification on the basis of sex, blood group, dominating racial character etc. is a structural classification.
Scientific classification on the basis of structural resemblance also reveals common invariable properties. Thus classificatory order is used in science to classify things on the basis of certain deep-seated functional similarities.
Though the process of classifying and cataloguing is the lowest level of order in science, still it widens our knowledge and deepens our understanding. For our knowledge of classification helps to know or infer the properties of the said class. So the process of classifying our experience will never be complete.
Some less developed sciences like genetics, psychiatry, life science etc. mostly follow this classificatory order.