The concept of function applied to human societies is based on an analogy between social life and organic life. The recognition of the analogy and of some of its implications is not new. In the nineteenth century the analogy, the concept of function, and the word itself appear frequently in social philosophy and sociology. So far as I know the first systematic formulation of the concept as applying to the strictly scientific study of society was that of Emile Durkheim in 1895. (Rules...)
     Durkheim's definition is that the “function” of a social institution is the correspondence between it and the needs... of the social organism. This definition requires some elaboration. In the first place, to avoid possible ambiguity and in particular the possibility of a teleological interpretation, I would like to substitute for the term “needs” the term “necessary conditions of existence”, or, if the term “need” is used, it is to be understood only in this sense. It may be here noted, as a point to be returned to, that any attempt to apply this concept of function in social science involves the assumption that there are necessary conditions of existence for human societies just as there are for animal organisms, and that they can be discovered by the proper kind of scientific enquiry.
     For the further elucidation of the concept it is convenient to use the analogy between social life and organic life. Like all analogies it has to be used with care. An animal organism is an agglomeration of cells and interstitial fluids arranged in relation to one another not as an aggregate but as an integrated living whole. For the biochemist, it is a complexly integrated system of complex molecules. The system of relations by which these units are related is the organic structure. As the terms are here used the organism is not itself the structure; it is a collection of units (cells or molecules) arranged in a structure, i.e. in a set of relations; the organism has a structure. Two mature animals of the same species and sex consist of similar units combined in a similar structure. The structure is thus to be defined as a set of relations between entities. The structure of a cell is in the same way a set of relations between complex molecules, and the structure of an atom is a set of relations between electrons and protons. As long as it lives the organism preserves a certain continuity of structure although it does not preserve the complete identity of its constituent parts. It loses some of its constituent molecules by respiration or excretion; it takes in others by respiration and alimentary absorption. Over a period its constituent cells do not remain the same. But the structural arrangement of the constituent units does remain similar. The process by which this structural continuity of the organism is maintained is called life. The life-process consists of the activities and interactions of the constituent units of the organism, the cells, and the organs into which the cells are united.
     As the word function is here being used the life of an organism is conceived as the functioning of its structure. It is through and by the continuity of the functioning that the continuity of the structure is preserved. If we consider any recurrent part of the life-process, such as respiration, digestion, etc., its function is the part it plays in, the contribution it makes to, the life of the organism as a whole. As the terms are here being used a cell or an organ has an activity and that activity has a function....
     To turn from organic life to social life, if we examine such a community as an African or Australian tribe we can recognise the existence of a social structure. Individual human beings, the essential units in this instance, are connected by a definite set of social relations into an integrated whole. The continuity of the social structure, like that of an organic structure, is not destroyed by changes in the units. Individuals may leave the society, by death or otherwise; others may enter it. The continuity of structure is maintained by the process of social life, which consists of the activities and interactions of the individual human beings and of the organised groups into which they are united. The social life of the community is here defined as the functioning of the social structure. The function of any recurrent activity, such as the punishment of a crime, or a funeral ceremony, is the part it plays in the social life as a whole and therefore the contribution it makes to the maintenance of the structural continuity.
     The concept of function as here defined thus involves the notion of a structure consisting of a set of relations amongst unit entities, the continuity of the structure being maintained by a life-process made up of the activities of the constituent units....
     By the definition here offered “function” is the contribution which a partial activity makes to the total activity of which it is a part. The function of a particular social usage is the contribution it makes to the total social life as the functioning of the total social system. Such a view implies that a social system (the total social structure of a society together with the totality of social usages in which that structure appears and on which it depends for its continued existence) has a certain kind of unity, which we may speak of as a functional unity. We may define it as a condition in which all parts of the social system work together with a sufficient degree of harmony or internal consistency, i.e. without producing persistent conflicts which can neither be resolved nor regulated.
     This idea of the functional unity of a social system is, of course, a hypothesis. But it is one which, to the functionalist, it seems worth while to test by systematic examination of the facts....
     The concept of function as defined above constitutes a “working hypothesis” by which a number of problems are formulated for investigation. No scientific enquiry is possible without some such formulation of working hypotheses. Two remarks are necessary here. One is that the hypothesis does not require the dogmatic assertion that everything in the life of every community has a function. It only requires the assumption that it may have one, and that we are justified in seeking to discover it. The second is that what appears to be the same social usage in two societies may have different functions in the two. Thus the practice of celibacy in the Roman Catholic Church of today has very different functions from those of celibacy in the early Christian Church. In other words, in order to define a social usage, and therefore in order to make valid comparisons between the usages of different peoples or periods, it is necessary to consider not merely the form of the usage but also its function. On this basis, for example, belief in a Supreme Being in a simple society is something different from such a belief in a modern civilised community....
     There is not, and cannot be, any conflict between the functional hypothesis and the view that any culture, any social system, is the end-result of a unique series of historical accidents. The process of development of the race-horse from its five-toed ancestor was a unique series of historical accidents. This does not conflict with the view of the physiologist that the horse of today and all the antecedent forms conform or conformed to physiological laws, i.e. to the necessary conditions of organic existence. Palaeontology and physiology are not in conflict.... Similarly one “explanation” of a social system will be its history, where we know it --the detailed account of how it came to be what it is and where it is. Another “explanation” of the same system is obtained by showing (as the functionalist attempts to do) that it is a special exemplification of laws of social physiology or social functioning. The two kinds of explanation do not conflict, but supplement one another.

     In the study of social structure the concrete reality with which we are concerned is the set of actually existing relations, at a given moment of time, which link together certain human beings. It is on this that we can make direct observations. But it is not this that we attempt to describe in its particularity. Science (as distinguished from history or biography) is not concerned with the particular, the unique, but only with the general, with kinds, with events which recur. The actual relations of Tom, Dick and Harry or the behaviour of Jack and Jill may go down in our field note-books and may provide illustrations for a general description. But what we need for scientific purposes is an account of the form of the structure. For example, if in an Australian tribe I observe in a number of instances the behaviour towards one another of persons who stand in the relation of mother’s brother and sister’s son, it is in order that I may be able to record as precisely as possible the general or normal form of this relationship, abstracted from the variations of particular instances, though taking account of those variations.
     This important distinction, between structure as an actually existing concrete reality, to be directly
observed, and structural form as what the field-worker describes....
     Social relations are only observed and can only be described by reference to the reciprocal behaviour of the persons related. The form of a social structure has therefore to be described by the patterns of behaviour to which individuals and groups conform in their dealings with one another. These patterns are partially formulated in rules which, in our own society, we distinguish as rules of etiquette, of morals and of law. Rules, of course, only exist in their recognition by the members of the society; either in their verbal recognition, when they are stated as rules, or in their observance in behaviour. These two modes of recognition, as every field-worker knows, are not the same thing and both have to be taken into account....
     Let us consider, for example, the study of law. If you examine the literature on jurisprudence you will find that legal institutions are studied for the most part in more or less complete abstraction from the rest of the social system of which they are a part. This is doubtless the most convenient method for lawyers in their professional studies. But for any scientific investigation of the nature of law it is insufficient. The data with which a scientist must deal are events which occur and can be observed. In the field of law, the events which the social scientist can observe and thus take as his data are the proceedings that take place in courts of justice. These are the reality, and for the social anthropologist they are the mechanism or process by which certain definable social relations between persons and groups are restored, maintained or modified. Law is a part of the machinery by which a certain social structure is maintained. The system of laws of a particular society can only be fully understood if it is studied in relation to the social structure, and inversely the understanding of the social structure requires, amongst other things, a systematic study of the legal institutions.
     I have talked about social relations, but I have not so far offered you a precise definition. A social relation exists between two or more individual organisms when there is some adjustment of their respective interests, by convergence of interest, or by limitation of conflicts that might arise from divergence of interests. I use the term “interest” here in the widest possible sense, to refer to all behaviour that we regard as purposive. To speak of an interest implies a subject and an object and a relation between them. Whenever we say that a subject has a certain interest in an object we can state the same thing by saying that the object has a certain value for the subject. Interest and value are correlative terms, which refer to the two sides of an asymmetrical relation.
     Thus the study of social structure leads immediately to the study of interests or values as the determinants of social relations. A social relation does not result from similarity of interests, but rests either on the mutual interest of persons in one another, or on one or more common interests, or on a combination of both of these. The simplest form of social solidarity is where two persons are both interested in bringing about a certain result and co-operate to that end. When two or more persons have a common interest in an object, that object can be said to have a social value for the persons thus associated. If, then, practically all the members of a society have an interest in the observance of the laws, we can say that the law has a social value. The study of social values in this sense is therefore a part of the study of social structure.

     I must say a few words about the spatial aspect of social structure. It is rarely that we find a community that is absolutely isolated, having no outside contact. At the present moment of history, the network of social relations spreads over the whole world, without any absolute solution of continuity anywhere. This gives rise to a difficulty which I do not think that sociologists have really faced, the difficulty of defining what is meant by the term “a society”. They do commonly talk of societies as if they were distinguishable, discrete entities, as, for example, when we are told that a society is an organism. Is the British Empire a society or a collection of societies? Is a Chinese village a society, or is it merely a fragment of the Republic of China?
     If we say that our subject is the study and comparison of human societies, we ought to be able to say what are the unit entities with which we are concerned.
     If we take any convenient locality of a suitable size, we can study the structural system as it appears in and from that region, i.e. the network of relations connecting the inhabitants amongst themselves and with the people of other regions. We can thus observe, describe, and compare the systems of social structure of as many localities as we wish.... 

      The view advanced in this Introduction is that to understand any kinship system it is necessary to carry out an analysis in terms of social structure and social function. The components of social structures are human beings, and a structure is an arrangement of persons in relationships institutionally defined and regulated. The social function of any feature of a system is its relation to the structure and its continuance and stability, not its relation to the biological needs of individuals. The analysis of any particular system cannot be effectively carried out except in the light of the knowledge that we obtain by the systematic comparison of diverse systems.
     All the kinship systems of the world are the product of social evolution. An essential feature of evolution is diversification by divergent development, and therefore there is great diversity in the forms of kinship systems. Some idea of the diversity of African systems can be obtained from the sections of this volume. Comparison of diverse systems enables us to discover certain resemblances. Some of these are features which are confined to one ethnic region. An example in Africa is the important part played by cattle and their transfer in the system of marriage and kinship. This is a feature of the patrilineal cattle-keeping peoples of East and South Africa from the Sudan to the Transkei. It is illustrated in this volume in Professor Wilson’s paper on the Nyakyusa. It would be valuable if some student could give us a systematic comparative study of the various customs of this kind. As an example of the kind of thing that is meant may be mentioned the custom in some parts of the Transkei that if a man drinks milk from the cattle of a lineage other than his own he may not thereafter marry a woman of that lineage; he is their kinsman through milk and cattle. In the same region the ceremony that completes a marriage is that in which the wife, who has usually borne at least one child, drinks for the first time the milk of her husband’s herd.
     There are other similarities of custom which, so far from being limited to one ethnic region, are widely distributed in parts of the world distant from one another. Customs of avoidance and joking between relatives by marriage are found in regions scattered all over the world. The custom of privileged familiarity of a sister’s son towards his mother’s brother is found in some peoples of Africa, Oceania, and North America. Then again the Swazi in South Africa and the Cherokee in North America both apply the term ‘grandmother’ (ugogo in Swazi) to all the women of the lineage or clan of certain grandparents (father’s father and mother’s mother in the matrilineal Cherokee, father’s mother and mother’s mother in the patrilineal Swazi) and give some measure of preference to marriage with such a ‘grandmother’. A general theory of kinship must be tested by the help it gives us in understanding or explaining these resemblances.
     For a kinship system to exist, or to continue in existence, it must ‘work’ with at least some measure of effectiveness. It must provide an integration of persons in a set of relationships within which they can interact and co-operate without too many serious conflicts. Tensions and possibilities of conflict exist in all systems. Professor Fortes and Dr. Richards have pointed out the tensions that exist in societies that approximate to mother-right. In systems approximating to father-right the tensions are different but exist none the less, as may be seen in the account of the Swazi. For a system to work efficiently it must provide methods of limiting, controlling, or resolving such conflicts or tensions. Dr. Nadel, in his paper on the Nuba, contrasts the Nyaro system, which he regards as providing an effective social integration, with the Tullishi system, which functions less efficiently. The Tullishi, he thinks, have been less successful than the Nyaro in constructing a well-ordered system of social relations, and he looks for the reason.
     Whether a kinship system functions well or not so well as a mode of social integration depends on the way it is constructed. Just as an architect in designing a building has to make a choice of structural principles which he will use, so, though in less deliberate fashion, in the construction of a kinship system there are a certain limited number of structural principles which can be used and combined in various ways. It is on the selection, method of use, and combination of these principles that the character of the structure depends. A structural analysis of a kinship system must therefore be in terms of structural principles and their application.