The definition of when a person becomes an adult varies according to culture, history, and discipline. In the English language a sequence is derived from etymology; "adult", from the French "adulte", from the Latin "adultus" ("grown up"), the perfect passive participle of adolescō ("I grow up"), itself from "adolescentem", the accusative form of "adolescens", present participle of "adolēscere" ("to become adult, grow up"), from ad- ("to") + alēscere ("to grow or become nourished"). With the subjectivity of individual differences it should be an uncontroversial point that individuals mature physically and cognitively at different ages.
A cultural or religious marker are various "coming of age" ceremonies which fit into the anthropological concept of "liminality", a transition from a pre-ritual status to a post-ritual status (Turner, 1974). Religous-cultural ceremonies are also a foundation in traditional law. For example, in the Christian tradition the Rite of Confirmation or anabaptism is usually at early adolesence, similar to the Judiac Bar and Bat mitzvah, and even in the secular form in Germany's secular "Jugendweihe". This can be compared to the provision of a courtesy name in East Asia, typically for men at aged twenty, and sometimes women typically at marriage (Wikinson, 2018).
Numerous cultural, legal, and historical examples are readily available which illustrate a wide divergence of the definition of when a person becomes an adult. Rather than engage in an extensive ethnological listing this essay will outline the methodological approach of formal pragmatics, conduct a literature review of some competing definitions, and apply a critical evaluation, before offering some useful conclusions.
Appropriate Methods
Determing an appropriate method to answer the question is requisite. Broadly speaking, there are two main paradigms in social inquiry, quantitative and qualitative. Quantitative methods will use empirical and objective measurements, with the use of mathematical or statistical analysis (Babbie, 2010). In contrast, a qualitative method approaches a problem from an interpretative standpoint, seeking to understand a subject's expressions in oder to provide understanding, meaning, narrative, and motivation (Bryman, 2016). If one takes a quantitative approach, the onset of adolescence could be marked with puberty with adulthood noted with the myelination of the prefrontox cortex and the pruning of synatic clusters by the mid-twenties. A qualitative approach, in contrast, could look both an individual subject's assertions on their own maturity or interpret their answers as representing cognitive competence in formal operations or the use of post-conventional moral reasoning (and if the latter is applied, many do not ever reach "adulthood").
With contradictory results one is tempted to use a mixed methods approach with caution to ensure an appropriate method selected according to the proposition raised. One example is formal pragmatics (Habermas, 1979). The philosophical framework of formal pragmatics is particularly appropriate as a logical method for selecting specific methods as it unites ontological and epistemological concerns. Formal pragmatics develops a rationalisation complex of ontological world orientations ("the objective world", "our intersubjective world", and "my subjective world") with specific epistemological verification claims (factual propositions, normative propositions, aesthetic propositions). For example, a factual proposition in the social world will differ from a normative claim, even on the same matter, as they have different means of verification.
A Literature Review
The method of formal pragmatics distinguishes between factual, normative, and aesthetic propositions, across objective, subjective, and intersubjective worlds. Starting with the factual statements relating to the objective world, a review of adulthood from the perspective of biology and neurology is required. Biologically, an adult is an living organism that has reached sexual maturity (McNamara, 2004, p262-263) or, to cite a medical dictionary, "the stage of the life cycle of an animal after reproductive capacity has been attained" (Becker, Landau, 1986, p52). Whilst such a stage was certainly common in traditional societies and even up to the early 20th century in advanced economies, contemporary society does not take such a view and as a result the term "biological adult" is used to distinguish from social adult (Gluckman, et al, 2006). Notably in this consideration accelerated physical growth with the onset of puberty reaches a peak on aveerage in the mid-twenties (Pringle et al 2016).
Neurologically, contemporary literature provides a different point of view to that of sexual maturity. In particular there is increasing recognition from longitudinal neuroimaging studies that stabilisation of brain plasticity from myelination of the prefrontox cortex and the pruning of synatic clusters continues well into the twenties, with the hypothesis that this can explain a higher degree of impulsiveness and lower levels of planning among adolescents, although it is recognised that "empirical evidence linking neurodevelopmental processes and adolescent real-world behavior remains sparse" (Johnson et al, 2009). Unlike biological adulthood where there is a relatively clear qualitative marker, neurological development is a more continuous process starting from birth onwards with different functional parts of the brain subject to different levels of maturation (Tierney et al, 2009).
In addition to physical facts, there are also social facts. Social facts are expressed as historical events, institutional rules, and positive law. The introduction to this inquiry gave a number of examples of different cultural markers for adulthood and these, are types of social facts. The "age of majority" is various contemporary jurisdictions is particular example, defined as a point when minors gain legal economic and contractual responsibility, which is 18 in most countries in the world. Whilst this is often used as the legal definition of adulhood, it is but one marker which can be associated with adulthood, and other relevant laws (such as the sexual consent, marriage, purchase of intoxicants, voting age, driving age, conscriptable age) will often be different from age of majority (Hamilton, 2016).
Positive law can be distinguished from socially normative law, the grounded moral reasons by which a positive law gains its legitimacy. In this sense in law is grounded in social norms and expressed in postive law as a social fact. The determination of that legitimacy will depend on the political system in place, the input of relevant experts, and the input of the population at large to the legislative process. In the latter sense, one can see that the social normative grounding of law is derived from an aggregation of subjective positions of normative morality, and the definition of when a person shows capacity for mature moral reasoning.
On this level one can review the classic studies of Piaget and Kohlberg in terms of capacity of formal operations and autonomous morality (Piaget), conventional and post-conventional reasoning (Kohlberg), albeit wth necessary modifictions to minimise liberal, western, and masculine biases (Gibbs, 2019). It is especially notable that the failure for many adults to reach post-conventional reasoning is deemed to be because of environmental reasons (Kuhn, 1977., Colby, 1983). It is necessary to also distinguish between the moral reasoning with moral learning as elucidated by social cognitive theory and moral emotions as provided by psychoanalytic theory. Moral reasoning, although a useful qualitative tool for understanding thinking processes it cannot in itself account for actual behaviour which, at the very least, must be at the level of conventional moral action in order for a functional society. An example of the difference can be illustrated in developmental studies in adolescent criminal behaviour (Cauffman et al, 2015)
In all these approaches there is individual variation expressed in aggregate as the kurtosis (e.g., Caravita et al, 2017). This statistical tool is raised not just to illustrate the need for nuance in making such an assessment of adulthood, but also to add understanding of sincere subjective claims by agents themselves. In this regard the question is when individual persons themselves believe themselves to have adult competence and deserve to be treated as such by others. Social competence self-assessment (Vaitkienė, Kiliuvienė, 2010) and evaluation of executive function performance (Zlotnik, Toglia, 2018) are important examples, along with variations based on internalised gender role expectations (Flannery, Smith 2017).
A Critical Evaluation
A critical evaluation and synthesis of the existing literature will provide a more definitive answer of when a person becomes an adult. A critical evaluation will tests validity of claims and identifies gaps. In a strong sense, the use of formal pragmatics includes some critical evaluation as a method, as it begins with the verification of different validity claims (truth, justice, sincerity) against different worlds (objective, intersubjective, subjective). This provides inoculation against some of the more common philosophical fallacies (e.g., it is difficult with formal pragmatics to engage in a naturalistic fallacy or a moralistic fallacy). Because the method seeks universal application to varied contexts, it is also unlikely to engage in contextually-bound structural claims (e.g., Tanner, Arnett & Leis, 2009) which conclude that "adulthood is achieved as a function of consolidation of identity around commitments to careers and families" and that "[e]merging adulthood is culturally bound existing 'in contemporary industrialized cultures that extend the transition to adulthood until the mid- to late twenties'", especially with the "American college experience and college environment are well-suited to the development features of emerging adulthood".
Instead of trying trying to shoehorn development reality into some Anglophone institutional norms of particular levels of technological development and a capitalist political-economy, a more nuanced approach will seek to find more universal claims that will fit in a greater diversity of cultural and historical contexts. Part of this must involve accepting a separation of domains and a recognition of individual diversity. It is beneficial therefore to follow the initial etymological distinction between "adolescent" and "adult", the former representing the _beginning_ of adult development which reaches an _end_ after the aforementioned physical growth period and neurological stabilisation. These biophysical characteristics (adolesence, adulhood), well-established in morphology, should be distinguished from the characteristics for formal operations and the moral reasoning and behaviour, that is, "maturity". Such qualitative changes in the thinking process should be reflected in qualitative changes to the brain (Quartz, Sejnowski, 1997). There is significant variations involved; human beings are a divergent species. In some cases people will have physical maturity without mental or beavioural maturity and vice-versa.
A further distinction can be made for domains where normative claims derive their validity. Again, an argument is made that domain specificity should be applied; "adulthood" is not something that is defined by a legal system or moral norms, but rather the verification is the existence of a legal right. The criteria of moral realism should still be applied, i.e., legal norms would reflect the insights from biological and neurological facts. One of these facts is the subjective variation among individuals. Whilst in most cases social systems apply an all-or-nothing approach (e.g., "at age X the following legal right is granted") with some edge-cases (e.g., people with intellectual disabilities who don't understand the content of a contract). Social systems with an age-based universal application are applied, at least in part, for resource allocation reasons. With improvements in productivity greater recognition of individual variation and respect to the right of agency could apply. In some cases, social rights could be subject to external verification, rather like citizenship tests (e.g., voting rights subject to a competency test of the political system). Ideally, the right time to grant social license depends on individual competence and understanding. It is questionable whether even the world of developmental psychology itself is even sure when this "right time" applies.
Conclusion
By raising the question of emerging adulthood definitional questions are raised. Recognising that there is cultural and historical variation in the application of the notion of adulthood, and individual variation on the key characteristics that are applied provides a significant challenge. One approach could be to simply acknowledge the variation and accept pure relativism as the criteria. However, if relativism is not compared to a standard then an inquiry becomes context-bound, rather than context-sensitive, in the inverse manner that what should be a nuanced universalism which has attention to detail becomes an crass absolutism.
Instead, this essay took formal pragmatics as a method and sought evidence against multiple verification claims. An evaluation of this literature recognised that what is conventionally called "adulthood" can vary not only to culture, history, and individual, but also to the domain of inquiry. Recognising these differences and their means of verification has led to the proposal that "adulthood" is a term best reserved for the biologists, and that this needs to be differentiated from "maturity" in cognition and behaviour, and "legal right" in terms of social norms. Such a proposal is contrary to the current state of affairs and is an idealised set of principles. Nevertheless, the approach provides for a greater accuracy and nuance on a question that is currently subject to political demagoguery and discomfort, a "problem" which deserves more careful and considered popular attention and psychological research.
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