Excerption is one of the functions of consciousness. Excerption means that you let a concrete aspect of a thing (such as a city's skyline) stand in for an abstraction (such as a city).
The problem comes in when someone insists on hanging on to an excerption in the face of other aspects of the thing, or even in direct conflict with a formal definition of the abstraction.
For example, thinking that evolution is the defining characteristic of life, as happened in DefinitionOfLife. Or thinking that hatred of people with different skin colours is the defining characteristic of racism, as happened in Iain Banks on BookShelved. Or thinking that Roman emperors are the defining characteristic of the Roman empire with all its people, cultures, actions and institutions, as happened on WikiPedia. Or thinking that the history of cars are the defining characteristic of all automobiles, as also happened on WikiPedia.
An opposing view is MeaningVsDefinition.
See also CargoCult