In this article I engage with the theoretical opening provided by Barry Buzan’s From International to World Society? I present an argument for five functional categories, which should be able to encompass all the institutions identified by English School scholars throughout history. Their introduction should point the way towards a sounder analytical framework for the study of what Buzan believes should be the new subject of the discipline of International Relations (IR). This subject is defined as second-order societies, meaning societies ‘where the members are not individual human beings, but durable collectivities of humans possessed of identities and actor qualities that are more than the sum of their parts’, and where the content of these societies, and the key object of analysis, is primary institutions. The purpose of the five functional categories is to break down this ‘social whole’ and provide a set of lenses through which to potentially analyse international societies throughout history.