This fallacy is committed when manipulations that are only possible on concrete things are said to be done on an abstract concept. The fallacy is also committed when an abstract concept is referred to as if it bore no relation to the concrete things that it is an abstraction of.
Note that this fallacy assumes the world-view of epistemological realism. Reification is not regarded as a fallacy by those who take up the viewpoint of epistemological idealism.
In knowledge representation, reification is sometimes used to represent facts that must then be manipulated in some way, for example to compare logical assertions from different witnesses to determine their credibility. The message "John is six feet tall" is an assertion of truth that commits the sender to the fact, whereas the reified statement, "Mary reports that John is six feet tall" defers this commitment to Mary. In this way, the statements can be incompatible without creating contradictions in reasoning.