An object can belong to many different，related categories. For example，the wooden object upon which you are sitting can be called by several different names：furniture，chair or desk chair. So we can see that categories arrange from level to level. Some category levels are called superordinate levels，which mean higher levels or more general levels. Furniture and animal are examples of superordinate category levels. Basic-level categories are more specific，but not too specific. Chair is an example of basic-level categories. Finally，there are subordinate levels，which mean lower levels or more specific categories. Desk chair is an example of subordinate categories. However， basic-level categories have a special status. Notice that there are differences between the terms prototype and basic-level category. A prototype is a best example of a category，whether the category level is superordinate，basic-level，or subordinate. It has been found that children learn basic-level words first，for the simple reason that they are not too general nor too specific and they are most useful. Basic-level categories are basic in three respects.

(i) Perception：overall perceived shape；single mental image；fast identification.

(ii) Communication：shortest，most commonly used and contextually neutral words，first learned by children and first to enter the lexicon.

(iii) Knowledge organization：most attributes of category members are stored at this level.

It is not hard to see that basic-level categories take primacy over categories at other levels. This is mostly because it is at this level that we perceive the evident differences between objects and organisms of the world. Most of the time，we understand superordinate categories with the aid of the features of basic-level categories. For instance， the comprehension of furniture comes from the collective properties of typical members like chairs，tables，desks，and beds at the basic level. Similarly，by the time a child can understand animal， he must have learnt cat，dog，lion， tiger，cow，and many others.