LEVELS OF ABSTRACTION
There's always a sort of invisible mental hierarchy present whenever anyone sets about to sort things into categories. Although culture and language play a big part in how someone's invisible hierarchy comes to be structured, one of the major factors that I.Q. tests measure is the degree of ability a person has in recognizing and naming the hierarchy in a certain way. In the English language, we refer to this hierarchy as levels of abstraction.
What are levels of abstraction?
In the case of the English language, the names of different categories are considered to be at an equal, higher or lower level to one another. Where these categories reside on that abstraction hierarchy depends upon the relative degree to which the things symbolized are similar and different.
For example, the similarities between two ants far outweigh the differences. The opposite is the case when we compare an ant with a eucalyptus tree. The word ant operates at a low level of abstraction. The word organism (which is what an ant is a kind of) operates at a high level of abstraction. Hen, chicken, fowl and animal operate at various levels of abstraction. Things named at low levels of abstraction have many characteristics (qualities) in common, and things named at high levels of abstraction have fewer characteristics (qualities) in common.