It's convenient to classify him as a writer of espionage fiction, because most of his protagonists are spies or people whose lives somehow have been redirected by contact with the secret world.
It is possible to give different identifiers to the two parts, but it is convenient to classify them as a large group to emphasize such rearrangements in the real genomes.
There are other several kinds of biological motors that can convert chemical energy into mechanical energy, and it is convenient to classify all of the biological motors we know about into five classes, which are not really mutually exclusive.
However, while it is convenient to classify interventions in this way, particularly when reviewing groups of interventions, in reality most interventions aimed at individuals or social groups are much more complex, with a single intervention often sharing elements with others in a separate classification.
From a toxicological point of view, it is often convenient to classify ingested ENMs (iENMs) as being either inorganic (such as TiO2, SiO2, Fe2O3, or Ag) or organic (such as lipid, protein, or carbohydrate), since the former tend to be indigestible and the latter are generally digestible.
It is conventional and convenient to classify fuels by their physical state, i.e. gases, liquids, and solids.
