Mental Health

Abstract

Mental health is a state of psychological well-being in which a person realises their abilities, copes with the normal stresses of life, works productively, and contributes to their community. Cognitive psychology and psychiatry increasingly treat it not as the mere absence of mental disorder but as a positive construct in its own right, with its own indicators and distribution across a population. The most influential reframing, the two-continua model, holds that mental health and mental illness are separate but correlated dimensions rather than opposite ends of a single line, so a person can carry a diagnosis and still function well, or be free of diagnosis yet languish. Positive mental health decomposes into hedonic components (feeling good) and eudaimonic components (functioning well), each with validated measures. This article sets out the construct, its measurement, its epidemiology, and effective interventions.

Keywords: mental health, well-being, two-continua model

Mental health, catalogued in the Medical Subject Headings as descriptor D008603, is the psychological counterpart to physical health: a positive state, not simply the absence of illness. The World Health Organization defines it as a state of well-being in which the individual realises their own abilities, can cope with the normal stresses of life, can work productively, and is able to contribute to their community. A working group of the European Psychiatric Association later sharpened this into a definition foregrounding the capacity for harmonious relationships, adaptive functioning, and self-regulation (Galderisi et al., 2015). The move from a residual definition — health as what remains when disorder is subtracted — to a substantive one is the central conceptual shift of the field (Keyes, 2007).

What Mental Health Is

For most of the twentieth century, mental health was defined negatively, as the absence of diagnosable mental illness. That residual definition has two defects. It gives no account of what a mentally healthy person positively possesses, and it implies, wrongly, that everyone without a disorder is equally well. The positive turn in the field replaced it with a construct that has its own content: the presence of positive emotion, psychological and social functioning, and the capacity to adapt (Galderisi et al., 2015; Keyes, 2007).

Defining the positive state is harder than defining its absence, and no single definition commands universal assent. A scoping review of the question found that expert definitions converge on a small set of features — well-being, adaptive functioning, autonomy, and the ability to form relationships — while disagreeing on whether temporary distress, which is often adaptive, should count against mental health at all (Fusar-Poli et al., 2020). What the definitions share is the insistence that mental health is a dimension along which the whole population varies, including the part of it that carries no diagnosis. This is the foundation of the positive psychology research programme and of public-health efforts that target well-being rather than only disorder.

The Two-Continua Model

The single most consequential idea in the modern study of mental health is that mental health and mental illness are not opposite ends of one continuum but two distinct axes (Keyes, 2002; Keyes, 2005). On the single-continuum view, adding health means subtracting illness; on the two-continua view, a person occupies a position on a mental-illness axis and, independently, a position on a mental-health axis, and the two are only moderately correlated. The empirical test is decisive: if the two were a single dimension, measures of well-being and measures of symptoms would correlate near −1.0, but they correlate far more weakly, and confirmatory factor models fit the data better with two latent factors than with one (Keyes, 2005; Westerhof & Keyes, 2010).

The model's practical yield is a two-by-two typology. A person can be free of mental illness yet low in well-being — languishing, a state of emptiness and stagnation that Keyes showed carries functional costs rivalling those of depression. A person can carry a diagnosis yet score high in well-being — flourishing despite illness. The two off-diagonal cells are exactly the cases a single-continuum view cannot represent, and they are common enough that the two-continua model is now embedded in national mental-health surveillance (Keyes, 2007). The model holds across the lifespan, with the same two-factor structure recovered from adolescence to old age (Westerhof & Keyes, 2010).

Hedonic and Eudaimonic Well-Being

The mental-health axis is itself composite. Two research traditions, with roots in two ancient conceptions of the good life, describe its parts. The hedonic tradition equates well-being with subjective experience — the presence of positive affect, the absence of negative affect, and satisfaction with one's life — and its canonical construct is subjective well-being (Diener, 1984). The eudaimonic tradition, descending from Aristotle, equates well-being not with feeling good but with functioning well: living in accordance with one's potential (Ryff, 1989).

Carol Ryff's model of psychological well-being gives the eudaimonic side six dimensions: self-acceptance, positive relations with others, autonomy, environmental mastery, purpose in life, and personal growth (Ryff, 1989). Self-determination theory supplies a complementary account, grounding well-being in the satisfaction of three basic psychological needs — autonomy, competence, and relatedness — whose fulfilment predicts intrinsic motivation and health (Ryan & Deci, 2000). Keyes folded both traditions, plus a social dimension, into a single tripartite structure of emotional, psychological, and social well-being, which is what his mental-health continuum measures (Keyes, 2002). The positive-psychology programme that Seligman and Csikszentmihalyi launched at the turn of the century gave this whole enterprise its institutional home and its research agenda (Seligman & Csikszentmihalyi, 2000). Seligman later advanced his own multidimensional account of flourishing, the PERMA model, which locates well-being in five measurable elements: positive emotion, engagement, relationships, meaning, and accomplishment. Empirical comparisons find that PERMA and subjective well-being track a largely overlapping but not identical construct, so the multidimensional and hedonic accounts converge without being redundant (Goodman et al., 2018).

Measuring Mental Health

Because mental health is a positive construct, it needs positive measures rather than symptom checklists run in reverse. The hedonic side is measured by scales of positive and negative affect and by satisfaction-with-life instruments; the Satisfaction With Life Scale, five items rated on a seven-point agreement scale, is the most widely used of these and has excellent psychometric properties across cultures (Diener et al., 1985). The eudaimonic side is measured by Ryff's Scales of Psychological Well-Being, which score each of the six dimensions separately (Ryff, 1989).

The Mental Health Continuum instruments operationalise the whole positive axis and, crucially, turn a continuous score into a categorical diagnosis paralleling the diagnosis of mental illness (Keyes, 2002; Keyes, 2005). A person is diagnosed as flourishing when they report high levels on at least one of the emotional-well-being items and on at least six of the eleven positive-functioning items; as languishing when they report low levels on at least one emotional item and at least six functioning items; and as moderately mentally healthy otherwise. This gives public health a categorical target — the prevalence of flourishing — that is not simply the inverse of the prevalence of disorder.

The Global Burden

The public-health stakes are large. Mental disorders are among the leading causes of disability worldwide: the Global Burden of Disease study estimated that mental disorders accounted for roughly 125 million years lived with disability in 2019, and remained among the top ten causes of burden globally, with no reduction since 1990 (GBD 2019 Mental Disorders Collaborators, 2022). Disorders are also common and begin early: the National Comorbidity Survey Replication found a lifetime prevalence of any DSM-IV disorder approaching one in two, with half of all lifetime cases beginning by age fourteen (Kessler et al., 2005). The economic cost is correspondingly vast, running to hundreds of billions of dollars annually in direct and indirect costs in high-income regions alone (Trautmann, Rehm, & Wittchen, 2016).

These figures measure the illness axis, but the two-continua model implies a second, hidden burden on the health axis: the large fraction of the population that is free of diagnosis yet languishing, and therefore at elevated risk and reduced function even though it never appears in disorder statistics (Keyes, 2007). A public-health strategy aimed only at treating disorder leaves this group untouched.

Promoting Mental Health

If mental health is a distinct axis, it can be raised directly, not only by treating illness. A meta-analysis of psychological interventions designed to improve well-being — including mindfulness-based, positive-psychology, and cognitive-behavioural approaches — found small-to-moderate effects on positive well-being that were largely independent of any effect on symptoms, exactly as the two-continua model predicts (van Agteren et al., 2021). The positive-psychology movement built an applied programme around such interventions, from gratitude and strengths exercises to programmes cultivating coping skills and resilience (Seligman & Csikszentmihalyi, 2000).

The population logic follows from Keyes's finding that flourishing protects: people who flourish have the lowest rates of subsequent mental illness, the fewest missed workdays, and the best physical health, so raising the prevalence of flourishing is a plausible primary-prevention strategy for mental illness itself (Keyes, 2007). This reframes mental-health promotion as a task distinct from, and complementary to, mental health services aimed at treatment.

Figure

Table

Note. The three components of positive mental health measured by the Mental Health Continuum, drawn from the hedonic and eudaimonic traditions and combined into a single categorical diagnosis of flourishing, moderate, or languishing (Keyes, 2002).

Worked Example

Consider how the Mental Health Continuum turns a set of symptom ratings into a categorical diagnosis. The short form presents fourteen items: three of emotional well-being and eleven of positive functioning (five social, six psychological), each rated on a six-point frequency scale from never to every day. A high rating means one of the top two categories (almost every day or every day); a low rating means one of the bottom two (never or once or twice) (Keyes, 2002; Keyes, 2005).

Take a respondent who gives a high rating to 2 of the 3 emotional-well-being items and to 7 of the 11 functioning items. The flourishing rule requires a high rating on at least 1 emotional item and at least 6 functioning items. Here 2 ≥ 1 and 7 ≥ 6, so both conditions are met and the diagnosis is flourishing. Now suppose the same person's functioning ratings were weaker: high on only 4 of the 11 functioning items. The emotional condition still holds (2 ≥ 1), but 4 < 6 fails the functioning condition, so the person is not flourishing. If they also give no low ratings sufficient to meet the languishing rule — which needs a low rating on at least 1 emotional item and at least 6 functioning items — they fall into neither extreme and are diagnosed as moderately mentally healthy. The break point on the functioning tally is therefore exactly 6: a respondent clearing the single emotional item flips from moderate to flourishing the moment their high-functioning count reaches 6 of 11. This categorical thresholding is what lets a public-health survey report the prevalence of flourishing as a number, independent of the prevalence of any disorder.

Discussion

The reconstruction of mental health as a positive, measurable construct — and its separation from mental illness into two correlated continua — is one of the clearest examples in applied psychology of a folk concept being rebuilt on empirical foundations (Keyes, 2005). It changed what public health measures, what interventions aim at, and how the field thinks about prevention: if flourishing protects against future illness, then promoting it is not a luxury adjacent to treatment but a component of prevention (Keyes, 2007).

The construct's difficulties are real and unresolved. There is no consensus definition of positive mental health, and a scoping review found experts disagreeing on whether values such as autonomy and productivity are universal or culturally specific, and on whether the definition should be value-laden at all (Fusar-Poli et al., 2020; Galderisi et al., 2015). A definition that prizes productivity and independence may mistake culturally particular norms for health. These are not reasons to abandon the positive construct but reminders that, unlike a fever, mental health is partly a normative judgement that psychology informs without fully settling.

Current Directions

Contemporary work runs along three lines. The first is definitional: efforts to fix a defensible, cross-culturally valid definition of positive mental health continue, with scoping reviews mapping the disagreements as a precondition for resolving them (Fusar-Poli et al., 2020). The second is interventional: meta-analytic evidence that well-being can be raised directly, and largely independently of symptom change, has shifted attention toward scalable, low-intensity well-being interventions and toward identifying which components of multi-part programmes actually carry the effect (van Agteren et al., 2021). The third is structural, extending the European reframing of the definition toward functioning, self-regulation, and the quality of relationships rather than affect alone (Galderisi et al., 2015). Across all three, the two-continua architecture is retained while its measurement and its cultural generality are refined.

Common Misconceptions

Mental health just means the absence of mental illness.

It is a positive state with its own indicators; a person can be free of any disorder yet languish, low in well-being and function (Keyes, 2005).

Having a mental illness rules out good mental health.

The two are separate axes; some people carry a diagnosis and still flourish, scoring high on well-being despite their symptoms (Westerhof & Keyes, 2010).

Mental health means feeling happy all the time.

Well-being combines feeling good with functioning well, and temporary distress in response to real adversity is compatible with, and often part of, healthy functioning (Ryff, 1989).

Mental disorders are rare.

Lifetime prevalence approaches one in two, and mental disorders are among the leading causes of disability worldwide (Kessler et al., 2005; GBD 2019 Mental Disorders Collaborators, 2022).

Glossary

Emotional well-being.

The hedonic component of the Mental Health Continuum: reported positive affect, happiness, and satisfaction with life.

Eudaimonic well-being.

Well-being conceived as functioning well and realising one's potential, in the Aristotelian tradition, rather than as pleasant feeling.

Flourishing.

The diagnostic category of high positive mental health, requiring high levels of emotional well-being and of positive functioning.

Hedonic well-being.

Well-being conceived as subjective experience — positive affect, low negative affect, and life satisfaction; the core of subjective well-being.

Languishing.

A state of low well-being and stagnation in the absence of mental illness, carrying functional costs comparable to those of depression.

Mental disorder.

A diagnosable clinical condition on the mental-illness axis, distinct from and only moderately correlated with the mental-health axis.

Mental Health Continuum.

A measurement model and instrument that diagnoses flourishing, moderate mental health, or languishing from tallies of emotional, psychological, and social well-being.

Positive functioning.

The psychological and social components of well-being — autonomy, mastery, purpose, integration, contribution — as distinct from emotional well-being.

Psychological well-being.

Ryff's six-dimension eudaimonic model: self-acceptance, positive relations, autonomy, environmental mastery, purpose in life, and personal growth.

Satisfaction With Life Scale.

A five-item self-report measure of the cognitive-judgemental component of subjective well-being, widely used across cultures.

Self-determination theory.

A theory grounding well-being in the satisfaction of three basic needs — autonomy, competence, and relatedness.

Social well-being.

Keyes's eudaimonic-social component: the sense of social integration, contribution, coherence, actualisation, and acceptance.

Subjective well-being.

The hedonic construct comprising life satisfaction and the balance of positive over negative affect, measured by self-report.

Two-continua model.

The account of mental health and mental illness as separate but correlated dimensions rather than opposite ends of one scale.

Key Researchers

Corey L. M. Keyes. Emory University. Introduced the two-continua model and the language of flourishing and languishing, and built the Mental Health Continuum that operationalises positive mental health as a categorical diagnosis.

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Carol D. Ryff. University of Wisconsin–Madison. Built the six-dimension model of psychological well-being that defines the eudaimonic side of positive mental health and its most widely used scales.

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Ed Diener (1946–2021). University of Illinois at Urbana–Champaign. Defined and operationalised subjective well-being, the hedonic core of mental health, and created the Satisfaction With Life Scale.

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Richard M. Ryan. Australian Catholic University. With Edward Deci, developed self-determination theory, grounding well-being in the satisfaction of the basic needs for autonomy, competence, and relatedness.

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Martin E. P. Seligman. University of Pennsylvania. Founded positive psychology, reorienting the field from repairing pathology toward building the strengths and positive states that constitute flourishing.

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Silvana Galderisi. University of Campania Luigi Vanvitelli, Naples. Led the European Psychiatric Association working group that produced an influential functional redefinition of mental health beyond the absence of illness.

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Ronald C. Kessler. Harvard Medical School. Directed the National Comorbidity Survey Replication, the epidemiological basis for population estimates of the prevalence and age of onset of mental disorders.

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Frequently Asked Questions

What is mental health?
Mental health is a state of psychological well-being in which a person realises their abilities, copes with normal life stresses, works productively, and contributes to their community. It is a positive state, not merely the absence of mental disorder (Galderisi et al., 2015).

Is mental health just the absence of mental illness?
No. The two-continua model shows that mental health and mental illness are separate but correlated dimensions, so a person can lack any diagnosis yet still languish, or carry a diagnosis yet flourish (Keyes, 2005).

What is the two-continua model?
It is the finding that mental health and mental illness form two distinct axes rather than opposite ends of one line; measures of well-being and of symptoms correlate only moderately, and two-factor models fit the data better than one (Keyes, 2002).

What is the difference between hedonic and eudaimonic well-being?
Hedonic well-being is about feeling good, meaning positive affect and life satisfaction, whereas eudaimonic well-being is about functioning well and realising one's potential; positive mental health combines both (Diener, 1984; Ryff, 1989).

What does flourishing mean?
Flourishing is the diagnostic category of high positive mental health, requiring high emotional well-being together with high positive functioning; people who flourish have the lowest risk of subsequent illness (Keyes, 2007).

How is mental health measured?
Through positive-construct instruments such as the Satisfaction With Life Scale for the hedonic side, Ryff's scales for the eudaimonic side, and the Mental Health Continuum, which yields a categorical diagnosis (Diener et al., 1985; Keyes, 2002).

How common are mental disorders?
Very common: lifetime prevalence of any disorder approaches one in two, half of cases begin by age fourteen, and mental disorders are among the leading global causes of disability (Kessler et al., 2005; GBD 2019 Mental Disorders Collaborators, 2022).

Can mental health be improved directly?
Yes. Psychological interventions raise positive well-being with effects largely independent of any change in symptoms, consistent with the two-continua view that the health axis can be targeted on its own (van Agteren et al., 2021).

References