The inter-relation of the work of state departments which makes co-ordination so necessary, also makes it difficult to invent categories which will enable the departmental system to be described without obscuring its outlines behind a mass of detail. In official reports, the four categories most commonly used are: Administration, Law and Order, etc.; Social Services; Development Services; Trading Services. The third of these categories includes departments with powers of control over industry, which it is more convenient to classify separately.

The first of these categories covers what might be regarded as the basic functions of the State—defence against external enemies and the maintenance of internal order—and in addition those services, such as finance, which are incidental to any complex social organisation. It might be arranged as follows: