As an ideology nationalism has, like the other concepts mentioned above, many variants and permits of no easy one-line definition. This is all the more so because, unlike most other political doctrine, nationalism has no clear founding theorist, no classical text which others can refer to, or argue about. It is what philosophers sometimes call a 'cluster-concept', i.e. an idea with several elements usually attached. One of the major analysts of nationalism, Anthony Smith, has provided a clear set of seven themes which comprise the core doctrine, what we can term here 'the cluster', of nationalist ideology.