1 INTRODUCTION

Our theoretical understanding of what care is and how to do it has been relatively neglected within traditional philosophical (e.g., Martinsen, 2006; Shields, 2013; Wiesing, 2008) and scientific discourses (e.g., Cook & Peden, 2017; Turkel et al., 2018). Despite the universal need for care across the lifespan—from birth to death—existing work has often been undertaken through a unidisciplinary lens or has focused solely on specific conditions, a distinct period of time along the developmental trajectory, or care provided in a specific setting by professional groups. Such approaches have served to limit the integration and spread of such work into professional and everyday caring activity, where care inevitably transcends multiple health disciplines, care contexts, and care needs (CNs) and conditions, and involves networks of people. Here, we define care as the provision of what is necessary for every person's survival, health, welfare, maintenance, protection or peaceful death.

Historically, caring practices have developed out of familial or community responsibilities, typically identified as women's work (Baines & Armstrong, 2019; MacDonald et al., 2005). In Western societies, care and caring moved into a wider societal or industrialised context with associated theoretical models, albeit unidisciplinary, emerging for understanding, describing and analysing care processes (Rehnsfeldt et al., 2017). Major paradigm shifts took place in the nineteenth century in industrialised societies when nursing became the professional group claiming caring as its core element (Rafferty et al., 2005). Indeed, several seminal nursing theories of self-care (S-C) and caring have been developed and continue to be taught as part of pre-registration nursing programmes globally. Examples of such theories include Orem's (2001) Self-Care Deficit Nursing Theory and Watson's (2008) Theory of Human Caring Science. These nursing theories have come under criticism for their limited relevance at the point-of-care and for providing little guidance on how caring can and should be achieved in practice (Mudd et al., 2020). These criticisms are not unique to nursing theories, with a theory-to-practice gap widely acknowledged across many health disciplines, including in medicine (Makransky et al., 2016), psychiatry and pharmacy (Pittenger et al., 2019) as well as in health policy and management (Chinitz & Rodwin, 2014).

Whilst discipline-specific theories in healthcare still have a role to play in providing professional autonomy, coherence of purpose, common professional communication and a rationale for practice (Colley, 2003; McCrae, 2012), unidisciplinary approaches to conceptualising care have their limitations. Unidisciplinary approaches can fail to fully explain the complex and dynamic factors affecting the delivery and enactment of care in different contexts and points of time and instead perpetuate siloed thinking and practice (Archibald et al., 2018; Urquhart et al., 2013). In comparison, interdisciplinary approaches have the potential to produce holistic conceptualisations of caring that synthesise and extend beyond discipline-specific perspectives and facilitate a more integrated understanding of CNs and care delivery. Importantly, many health disciplines in addition to nursing are becoming increasingly interested in the concept and articulation of caring as the basis of healthcare delivery. For instance, in health economics and policy, the notion of a ‘care economy’ outlines the importance of measuring, valuing and investing in paid and unpaid care work that occurs within professional settings and across families and communities (Folbre, 2018). Developing a strong, equitable care economy is argued to be crucial for ensuring safe, appropriate care for an ageing population and people with disabilities, chronic conditions, or multimorbidity, as well as to support gender equality relating to employment and economic empowerment (International Labour Office, 2018; Power, 2020). However, we have yet to find a systematic way of integrating diverse disciplinary perspectives on caring to achieve the vision of integrated, holistic person-, family- and community-centred care.

Further, although care has emerged from the privacy of personal relationships and households and is now embedded within the epistemological foundations of different health disciplines, it continues to be perceived as a ‘soft’ skill, linked to innate qualities (e.g., patience and empathy) or even to common sense, rather than a validated empirical base of caring practices (Feo et al., 2019; Treiber & Jones, 2015). As a result, the systematic study of care and caring practices has been little evident in many health and medical curricula, despite the trend to move such curricula from a traditional biomedical structure to more person-centred, biopsychosocial models of care that focus on relationships, trust and participation (Borrell-Carrió et al., 2004). This is coupled with a pervasive narrative in current policy that care interventions constitute costs to society rather than constructive humane solutions for social and economic prosperity (Ratcliffe et al., 2020). Investing in a ‘care economy’ is therefore not seen to deliver financial benefits, with much-needed funds instead diverted elsewhere (De Henau et al., 2016). However, with the advent of person or patient-centred care (Kitson, et al., 2013); the need to promote better S-C and self-management practices (Grady & Gough, 2018; Jaarsma et al., 2020; Richard & Shea, 2011); and the unprecedented changes brought about by COVID-19, including new ways of providing care, such as telehealth, and the increased care burden on women, families and communities (Power, 2020), we must clarify what we mean by care and S-C and how these can best be operationalised from an interdisciplinary perspective and drawing upon relevant theoretical insights.

In addition to reconceptualising and providing a stronger theoretical foundation for S-C and caring that transcends health disciplines, there is an imperative to advance our theoretical thinking about the antecedents, interdependencies and consequences of care specifically from a lifespan perspective. Our ageing population, embedded ageist attitudes, increasingly complex health and CNs, and growing evidence that chronic disease risk starts from birth are well known facts (Ham et al., 2017; Masic, 2018; World Health Organisation, 2018). Yet we have not systematically embedded this evidence into theoretical conceptualisations of care. Instead, robust care theories tend to focus on condition- or situation-specific scenarios (e.g., Riegel et al., ,2012, 2016). In turn, this has limited our ability to develop effective solutions to balance CN across the lifespan with affordable and appropriate care provision (CP). Whilst life-course perspectives have been used to explain childhood and adulthood development (e.g., Elder & Shanahan, 2007), chronic disease epidemiology (e.g., Ben-Shlomo et al., 2016), sociological responses (e.g., Shanahan, 2000), human cognitive abilities and decline (e.g., Anstey, 2012), and ageing (e.g., Cooney & Curl, 2019), such perspectives have not, to date, been used to frame how individuals learn to care for themselves and for others.

As a response to the unprecedented changes in individual and global health and CNs, and the changing nature of CP, this paper presents a novel, theoretically robust way of describing a person's CNs across the life course, both from their own perspective and from the perspective of care providers. Life course in the context of our proposed caring life-course theory (CLCT) refers to the life stages a person transitions through across the lifespan, taking into account structural, cultural, social, health and temporal factors that affect care (cf. Elder, 1994). The dual emphasis on social structure and (individual and collective) human agency, as well as the interdependencies across multiple levels of analysis (i.e., from ‘micro’ to ‘macro’), life domains (e.g., education, family and work) and interrelationships between people (e.g., the linked lives of family, friends and colleagues) are compatible with the central principles of a care life-course perspective. We build upon the empirical work of Kitson and colleagues around the fundamentals of care framework (Kitson, et al., 2013; Kitson & Muntlin Athlin, 2013), which provides the practical scaffolding for defining a person's universal CNs (i.e., CNs essential for survival, health, well-being, maintenance, protection or peaceful death) across the lifespan and which also has its provenance from seminal nursing work such as Henderson (2004) and Roper et al. (2001).

2 DESIGN

We drew on inductive approaches to theory generation and refinement and upon the authors' diverse clinical, research and academic experiences to critically challenge our assumptions and knowledge around care. We wanted to explore more integrated, theoretically robust ways of describing S-C and caring interventions that would not just reflect the complexity and contingent nature of caring relationships but also offer new insights into more transparent, sustained and collaborative ways of working between informal and professional carers and people needing care.

We also used the empirical methods from previous work (Feo et al., 2018; Kitson, et al., 2013; Kitson & Muntlin Athlin, 2013) as the basis upon which to define CNs. The first author was responsible for proposing that the fundamentals of care framework be located within a life-course perspective and presented several ideas to the wider group at a series of collaborative weekly meetings over a 6-month period (March 2020–August 2020).

During these meetings, the wider interdisciplinary team shared their knowledge and experiences of thinking about and researching care and S-C. The lead author presented initial constructs and these ideas were interrogated and challenged by the whole team until such time consensus was reached and no more new ideas or perspectives emerged. This constant refinement and interrogation were supplemented with a targeted review of relevant theories from a range of disciplines (e.g., Sen's Capability Approach, Theory of Planned Behaviour, Erikson's stages of psychosocial development). Detailed notes were taken at each meeting with a synthesis of ideas presented at the following meeting together with the critiquing of relevant literature appropriate to the construct being interrogated.

The meetings provided rich discussions, which were documented in detail by the first and second authors. Meetings continued until the team had reached saturation in terms of ideas and consensus on the core concepts of the theory, with empirically derived examples (where possible) used to illustrate the constructs and test the face validity of the emerging theory.

3 PRESENTING THE CLCT: THE BASIC BUILDING BLOCKS

From our deliberations, using the empirical work of the fundamentals of care framework as the starting point, we generated several core constructs, summarised in Table 1. We define these constructs sequentially, building up a narrative that explains how the theory could be used to articulate the contribution of care to people's health and well-being across the lifespan.

TABLE 1. Summary of caring life-course theory building blocks/constructs Construct Definition Fundamental care The care required by everyone for survival, health, welfare, maintenance, protection or peaceful death, regardless of the presence or type of clinical condition or the setting in which care is taking place. Life course The life stages, transitions and trajectories in health and well-being across the lifespan from birth until death. Care network The relationships and support mechanisms surrounding individuals and their families and friends. Care need (CN) A fundamental care need—physical, psychosocial or relational—throughout the lifespan met by oneself or by others. Care provision (CP) How care needs are met—i.e., through the enactment of care activities either by oneself or by others. Self-care (SC) Tasks intentionally performed by individuals to address their own care needs, maintain health and well-being, prevent and manage illness and attain specific goals. Care-from-others (C-Fm-O) Care actions or processes received from others to address a person's care needs. Care-for-others (C-Fr-O) Care actions or processes provided to address another's care needs. Care Provision Package The full complement of care required to be provided for a person, made up of a combination of self-care and care from informal, formal or professionals carers. Capability The ability (skills, knowledge and motivation) to care for oneself and others throughout the life course. Capacity The amount/volume of care available to oneself and others throughout the life course. Care transition An event or life stage that triggers a change in a person's care needs. Care trajectory The potential impact a life event might have upon a person's self-care and care-for-others capability and capacity. Care biography A personalised history of an individual's self-care and caring capability and capacity and their understanding of the care they have and should receive from other people. 3.1 Fundamental care

The primary building block of the CLCT, which provides the theory its scaffolding structure, is the fundamentals of care framework (Kitson, Conroy, et al., 2013). Fundamental care refers to the care required by everyone for survival, health, welfare, maintenance, protection or peaceful death regardless of the presence or type of clinical condition or the setting in which care is taking place. The framework is designed to conceptualise and articulate these fundamental—that is, universal—needs and how care for these needs is best provided. The framework defines fundamental care as involving three key dimensions: (1) the relationship between care provider(s) and recipient(s); (2) the integration and meeting of a range of CNs simultaneously (physical, psychosocial and relational); and (3) the context in which CP is taking place (Figure 1). The framework can be used to identify both CNs and provision as they occur in each life stage or pertinent transition across the life course (e.g., infancy, adolescence and parenthood).

The fundamentals of care framework (Kitson, Conroy, et al., 2013) 3.2 Life course

The term life course refers to the life stages, transitions and trajectories in care across the lifespan from birth until death (cf. Elder, 1994). A life-course perspective necessitates attention to the passage of time and temporal phenomena. At an individual level, time is constituted in chronological age and life stages. Broadly speaking, life stages span: infancy, early childhood, middle childhood, adolescence, young adulthood, middle adulthood and late adulthood, reflecting Erikson's stages of psychosocial development (Erikson & Erikson, 1998). At a societal level, time might be represented in terms of family and historical generations (i.e., intergenerationality). The CLCT therefore takes account of structural, cultural, social, health and temporal factors that affect care and CP.

3.3 Care network

The CLCT acknowledges that people are inherently social beings and hence health and well-being, as well as CNs and provision, must also be understood as inherently social activities, predicated on and impacted by a person's relationships. Care network thus describes the set of relationships and support mechanisms surrounding individuals, their families and friends. These care networks are linked to social and familial bonds as well as cultural, generational and other ties.

3.4 Care need

A CN refers to a fundamental CN—which can be physical, psychosocial, or relational, or in any combination—occurring at any point in the lifespan. As outlined above, a fundamental CN refers to a need that all individuals have, irrespective of age, health or context, to keep a person alive and in optimum health and well-being or to support them in a peaceful death. CNs can be met by oneself and by others. Consistent with the fundamentals of care framework (Kitson, Conroy, et al., 2013), this conceptualisation of CN takes account of the context where care is delivered, whether it be in one's own home, the community or in a formal care setting. A person's CNs vary across the life course and are influenced by intrinsic (e.g., genetics and behaviours) and extrinsic factors (e.g., environment, medical care and social). Importantly, a person's CNs do not diminish their intrinsic worth or ability to lead a fulfilled life; rather, the lack of appropriate care impacts their lived experience.

3.5 Self-care

We define S-C broadly as tasks intentionally performed by individuals to address their own CNs, maintain health, prevent and manage illness or directed towards other specific goals (Grady & Gough, 2018). S-C encompasses skills, knowledge and attitudes around fundamental CNs, forming and sustaining positive relationships and managing resources to promote the meeting of S-C needs (Matarese et al., 2018). S-C can also be supported by digital health technologies, including gamification, behavioural nudging and incentivisation strategies designed to enable the adoption and maintenance of health-seeking behaviours and lifestyle choices (Johnson et al., 2016).

3.6 Care-from-others

Care-from-others (C-Fm-O) refers to actions or processes received from others to address a person's physical, psychosocial and relational CNs. C-Fm-O encompasses a person's willingness to accept and receive care from another, and their ability to articulate how that care should be delivered. It is CP from the care recipient's perspective. There are different sources of ‘other carers’: informal (e.g., family); formal (i.e., paid); and professional carers (e.g., health and social care workforce), with each supported by technology where relevant.

Taking the above into consideration, CNs can be represented across the lifespan as in Figure 2.

Proportion of care needs (CNs) met through self-care (S-C) and care-from-others (C-Fm-O) throughout the lifespan

Figure 2 offers a novel way of thinking about the proportionality of CNs that can be met by oneself and by others, across the lifespan. Moving from the private world of care from parents and families, we suggest there is a pattern of developmental trajectories with typical/atypical attributes and associated CNs. In the early stages of life, it is self-evident that infants and young children are highly dependent upon C-Fm-O (e.g., mother, father, grandparents, extended family and professionals) to meet their CNs. In Figure 2, at this stage, the proportion of C-Fm-O is depicted as high relative to the individual's S-C capability and capacity. Childhood development theories (e.g., Bandura, 1997; Bowlby, 1988; Erikson & Erikson, 1998; Piaget & Inhelder, 1969; Vygotsky, 1994) outline the expected trajectories of the development of S-C capabilities and capacities, theoretical perspectives that the CLCT can build upon.

Equally, there is an expectation that as children develop into adolescence and early and mature adulthood, they will have mastered the skills of S-C sufficiently such that they require less help from others. CNs then increase as individuals age and require more support to help with the various comorbidities and life events that might compromise their ability to care for themselves or when established care networks can no longer provide the care needed by the individual.

Successful or appropriate CNs being met for individuals could be summarised in the following way:

OR

In other words, a variable proportion of a person's CNs will be met by themselves and others according to their capabilities, developmental level and available support networks.

3.6.1 Under what conditions would we expect CNs to vary?

CNs vary according to a range of intrinsic and extrinsic factors related both to the person who needs the care and the care network that surrounds them, within a particular spatial and temporal context. We know that CNs vary across different clinical populations and health conditions (e.g., people living with multiple comorbidities, or disabilities, or mental health issues) and that socio-economic conditions, such as poverty, unemployment, migration or isolation, impact care (Nelson et al., 2019; Rasanathan et al., 2011; World Health Organisation, 2015).

Figure 3 represents two ‘archetypes’—a person whose majority of CNs are required to be met by others rather than by themselves (top line) due to several intrinsic factors that could relate to genetic or behavioural pre-dispositions. The bottom line represents a care trajectory that might reflect the CNs of a person living with multiple comorbidities from middle life, where several extrinsic factors have shaped their ability to S-C and their need for C-Fm-O.

Proportion of care needs (CNs) met through self-care (S-C) and care-from-others (C-Fm-O) throughout the lifespan, taking account of intrinsic and extrinsic factors

These variations in the proportions of S-C and C-Fm-O required to meet a person's CNs could also be represented in the formula: OR

However, the proportions of S-C and C-Fm-O would differ between groups, across the life course and at specific points in time. Regardless of these differences, the CLCT operates from a position that every person has the right to have their CNs met, regardless of the proportion of S-C or C-Fm-O. This means there is no discrimination towards individuals who need more help from others; rather, it is a societal responsibility to allocate resources and support accordingly.

3.7 CP: How CNs are met

In the CLCT, CNs are met through adequate and appropriate CP. CP is defined as the enactment of care abilities and activities either by oneself or by others to address individuals' physical, psychosocial and relational needs at a given point in time in a wider historical and socio-political context.

An optimal care scenario could be summarised as follows:

That is, an individual's CNs are satisfied through a combination of S-C and C-Fm-O provision. Figure 4 considers two hypothetical situations: what happens when the CNs of an individual are not met—that is, there is a deficit in terms of S-C or C-Fm-O. The top hatching represents S-C deficits, and the bottom hatching illustrates deficits in C-Fm-O.

Unmet care needs highlighting self-care (S-C) and care-from-others (C-Fm-O) deficits

The deficit in either S-C or C-Fm-O influences how the person's CNs are met across the lifespan. For example, if we consider the top left-hand hatched area in Figure 4 (labelled ‘A’), this S-C deficit emerging in infancy might be related to developmental delays leading to the child being unable to self-feed or to articulate CNs effectively. If this S-C deficit is not recognised or addressed by additional C-Fm-O to compensate, then the S-C deficits are likely to continue and affect other S-C capabilities, potentially manifesting in additional issues and needs at subsequent developmental stages.

If C-Fm-O at infancy (Figure 4; labelled ‘B’) was deficient, either in terms of meeting self-CNs or a more complex set of delayed developmental issues, then the CNs of the infant would be considerably compromised. Such a scenario could be a teenage mother who gives birth to a pre-term child and has little support to care for their child, loses her job and/or experiences homelessness. What will the caring trajectory of this scenario look like across the lifespan for mother and child? What additional education and support would be required to enable the infant, mother and wider care network to provide optimal care across the life course?

The situation in Figure 4 could generate three possible scenarios:

i) CN > CP (S-Clow + C-Fm-Oacceptable), as illustrated by hatched area ‘A’ (Figure 4).

Here, we conjecture that a person who has deficits in S-C, which are not detected early or throughout their life course, will generate a continued S-C deficit throughout the lifespan and, potentially, across different life domains. Consider, for example, a young child who has diabetes and whose parents take primary responsibility for his care in relation to disease management. Despite this support, the child is not taught by his parents or other carers how to manage his condition independently. The child therefore does not develop requisite S-C skills that will ensure his health and well-being when his parents no longer have primary responsibility for his care. As such, he will likely have CNs that are not met in later life because of a limited ability to enact appropriate S-C behaviours.

ii) CN > CP (S-Cacceptable + C-Fm-Olow), as illustrated by hatched area ‘B’ (Figure 4).

Here, we can consider the possibility of a teenager who, through her schooling, learns the importance of diet and exercise for maintaining physical and mental health. Through this knowledge, she can undertake appropriate S-C activities to support her health and well-being, including making healthy food choices at school. However, the ability to maintain these behaviours is impacted by her home life and an unstable job market, which limits the family's finances, ultimately impacting food choices.

iii) CN > CP (S-Clow + C-Fm-Olow)

Our earlier example of the infant with developmental delay and with a primary carer who is experiencing significant challenges in S-C, would exemplify the situation where CNs are greater than both S-C and C-Fm-O. When these care deficits emerge early in a child's life and are not mitigated, they can have lasting effects upon their S-C, leading to potential health and well-being challenges later in life and impacting their ability to care-for-others (C-Fr-O). Equally, the deficits in CP from others, whether informal, formal, or professional carers, will generate a series of consequences that build momentum over time.

There are also three scenarios that are theoretically possible around CP being greater than CNs:

i) CN < CP (S-Cacceptable + C-Fm-Ohigh)

This could be a situation where an individual can care for themselves but is receiving excessive C-Fm-O that is disproportionate to their CNs. An example could be a carer who is overprotective of their elderly parent and limits the amount of socialising their parent engages in for fear of them falling. This behaviour not only provides excess care but also has the potential to undermine the S-C of the older person.

ii) CN < CP (S-Chigh + C-Fm-Oacceptable)

In this scenario, we might think about a young adult who is overly conscious of hygiene issues, such that they develop compulsions around hand hygiene and cleanliness and subsequent fears of socialising. Whilst they might have successfully hidden this emerging S-C challenge from others in their care network, it will reach a point where their excess vigilance in terms of S-C will start to challenge their daily life. Whilst there are known approaches to managing this phenomenon (Heyman et al., 2006), it is unlikely that a care lens has been used to understand the genesis of the behaviour or how caring practices might change it.

iii) CN < CP (S-Chigh + C-Fm-Ohigh)

This scenario could reflect a person with a tendency towards hypochondria, where they overregulate their own care and regularly seek care from informal, formal, and professional sources. Again, understanding this phenomenon from a CN and CP perspective, positioned within a life-course lens, might shed light on some S-C and care-from-other practices and importantly consider novel interventions that could be tested.

3.8 Care-for-others

We now shift the construct C-Fm-O, as experienced by the person receiving care, to C-Fr-O, to describe the experiences of people who choose or are requested to provide care for others. This dual perspective—care from and care for—emphasises and reinforces a central tenet of the CLCT; that all care transactions must be negotiated between the person receiving care and person providing care before CNs can be met optimally. This principle is highly complex to execute given the levels of dependency, advocacy, self-efficacy, agency and social and cultural norms that must be considered as care is negotiated throughout the lifespan and between individuals and networks.

Within the CLCT, C-Fr-O is defined as care actions or processes provided by others to address a person's physical, psychosocial and relational CNs. As outlined above, people who provide C-Fr-O include informal (family, friends, unpaid carers), formal (paid carers) and professional carers (health, medical, disability and social care workforce), each supported by various types of technologies.

Figure 5 acknowledges the dominant presence of informal CP in infancy and childhood years, with an expected decline in all types of C-Fm-O throughout adulthood due to S-C abilities and resources being developed and utilised. As people grow older and acquire more comorbidity or disability, so the proportion of C-Fm-O is expected to increase from all CP types in later years. For many individuals, most CNs will be met primarily by self or by informal carers. However, a life transition such as pregnancy, puberty or retirement might create additional CNs that cannot be met by self or informal carers within the individual's care network, and formal and professional carers might be required to provide the additional care.

How care needs (CNs) are met by others

3.9 Care provision package

Care is rarely, if ever, provided by an individual alone or in isolation. We thus propose the Care Provision Package (CPP) as a construct to describe the full complement of agents involved in CP for an individual. The CPP comprises of a combination of the individual who is engaged in S-C as well as informal, formal and professional carers. Whilst the CPP focuses primarily on the individual (or teams) providing care, this construct can be expanded to include the full scope of CP, including technological and pharmaceutical interventions.

There are two additional constructs within the CLCT that relate to CP. These are Capability and Capacity, each described below.

3.10 Care capability

Care capability refers to the ability (i.e., skills, knowledge and motivation) to care for oneself and others throughout the life course. Capabilities cover relationship-enabling, knowing, decision-making, operational and doing capabilities that enable people to maintain good health and prevent illness in themselves and those they care for.

Care capability comes in two main forms: S-Ccapability, the ability to care for oneself. C-Fr-Ocapability, the ability to care for others.

The CLCT postulates a third form of care capability: care-from-other capability, a person's ability to intentionally search for, ask for or acquire assistance from selected sources of care to address an identified need. The ability to identify and recognise personal CNs is dependent on a person's physical, cognitive and psychosocial developmental levels, as well as their health and digital literacy. Further, care-from-other capability is likely to be dependent on individuals' readiness to voluntarily seek and accept care from a chosen carer.

3.11 Care capacity

Care capacity refers to the amount or volume of care available to oneself and others throughout the life course, limited by time and resources, and other factors in the context of the person's social/medical environment, such as access to services, availability of informal/formal care networks, geographic location, poverty, stigma and discrimination. Capacity focuses on the individual in their context and how that context enables or limits them to provide care for themselves or to others.

Care capacity comes in two main forms: S-Ccapacity, the amount of care that a person can provide to themselves. Care-for-other capacity, the amount of care that a person can provide to others.

An additional form of care capacity is C-Fm-O capacity, the amount of care a person can successfully seek, ask for or gain from others, limited by, for example, time, money, access to healthcare services, availability of technologies, and remoteness.

Care capability and capacity need to be evaluated and re-evaluated for each individual across the lifespan. Consider a single parent who has lost their job and is caring for two young children and an elderly relative. Whilst they might have been able to manage, both in terms of capability and capacity, before the job loss, they are now in different socio-economic circumstances. They might no longer have capacity to provide C-Fr-O in their network, and require additional support, such as from informal carers (relatives, neighbours or friends). Likewise, if one of their family members becomes more dependent (e.g., the elderly relative falls and requires restorative care), the parent might not have the capability to care for the family member's increasingly complex needs and will require formal or professional support.

According to the CLCT, a person will have a range of S-C capabilities and capacities that will vary across the life course. They might be able to cope well at one point in their life but then due to intrinsic or extrinsic factors, are no longer able (i.e., lack the skills, knowledge and/or motivation) or do not have the resources to look after themselves (e.g., they might have been made unemployed or experiencing bereavement following the loss of a partner). This is where an understanding of life-course care transitions (i.e., significant points of change) and care trajectories (i.e., anticipated CNs based on the assessment of S-C capability and capacity) add a predictive element to the theory.

3.12 Care transition

A care transition is an event or life stage that triggers a change in a person's CNs. The event might be intrinsic (e.g., puberty, pregnancy and fatherhood) or extrinsic (e.g., unemployment, retirement and coping with a natural disaster) in nature. Such events impact upon a person's S-C, C-Fm-O and C-Fr-O capability and capacity.

3.13 Care trajectory

Care trajectory relates to the potential impact a life event might have upon a person's S-C and C-Fr-O capability and capacity. Health and care professionals are most likely to be involved in life-course situations where an event triggers a need for more care (care transition) or when an event creates a different set of CNs for the future (care trajectory). To assess a person's CNs accurately at these critical points in time, it is important to collate the care information in what we call a care biography.

3.14 Care biography

A care biography refers to the personalised history of an individual's S-C and caring capability and capacity and their own understanding of the care they have and should receive from other people. A care biography is equivalent to a personalised health record in that it should record, across the life course, a person's S-C capability and capacity and their preferences in how care is provided for them. It should also help them and their carers plan care following certain negotiated care trajectories. This information would be owned by the individual and used to negotiate care in each care encounter. Importantly, the care biography should also record each person's care network, identifying their key carers and those for whom they care over their life course.

4 DISCUSSION

We propose the CLCT as a unifying theory that incorporates understandings from multiple disciplines; philosophical and epistemological orientations; and existing theories, models, and conceptual frameworks. Seminal nursing theories of care share similarities with the CLCT in that they describe fundamental aspects of caring and S-C, including the nurse-patient relationship (e.g., Nursing Process Theory; Orlando, 1961); integration of care (i.e., simultaneously addressing a persons' physical, psychosocial, and relational needs) (e.g., Person-Centred Nursing Framework; McCormack & McCance, 2006); and the context of care (e.g., Sunrise Model; Leininger & McFarland, 2002) at microlevel (individual factors), mesolevel (organisational factors), and macrolevel (environmental factors). Yet, extant theories generally do not depict these aspects collectively and often describe the integration of the physical, psychosocial and relational aspects of care poorly (Mudd et al., 2020). Comparable to the CLCT, the Self-Care Deficit Nursing Theory (Orem, 2001) posits that S-C deficits can occur when care demands exceeding S-C agency. In addition, and similar to the CLCT, the Theory of Human Caring Science is a relational theory of care that aims to “protect, enhance, promote, and potentiate human dignity, wholeness, and healing, wherein a person creates or cocreates his or her own meaning for existence, healing, wholeness, and living and dying” (Watson, 2010, p. 327) through intentional, meaningful, and authentic interactions or ‘caring moments’.

Unlike these theories, however, the CLCT is designed to acknowledge and incorporate but also to transcend context or the perspective of any single agent (i.e., the person[s] receiving care vs. the person[s] proving care). That is, it is designed to explain people's care and S-C needs as they occur across the lifespan, rather than within the confined parameters of specific care contexts, health conditions or societal structures. This is achieved by focusing on a person's care and S-C in terms of both their current context (e.g., current CNs, capability and capacity for S-C, relationships, and broader socio-political context) and their lifespan (e.g., their own personal experiences and histories). We also want to generate a unifying discourse around care and S-C that enables different professional disciplines as well as the public to get involved in tackling some of our most challenging care issues, such as improving aged care and caring for people with disabilities to enable them to have respectful, productive, fulfilling lives.

In this discussion, we reflect upon our journey around generating and refining the constructs underpinning the CLCT and highlight areas of continued debate and uncertainty. We consider potential unintended ways that the CLCT could be used, which might not improve people's experiences of care. Despite these potential misuses, we argue there are more benefits than risks in continuing to explore this theoretical path. The discussion concludes by identifying a range of issues that need to be explored if the theory is to be further refined and tested to have practical impact.

4.1 Our reflective journey

As outlined in the methods section, we represent a diverse philosophical, theoretical and multidisciplinary research team. This diversity has helped us to generate a unique shared understanding around S-C and caring interventions. The CLCT has enabled us to understand and interpret our own research successes—and failures—in more integrated, dynamic ways.

For example, Golley and colleagues' work on child obesity prevention (Golley et al., 2011; Seidler et al., 2020) highlighted the importance of interventions that aimed to enhance parental capacity to establish healthy family lifestyle beha