Two Theories of Human Motivation Are Finally Being Mapped Onto Each Other

In the crowded landscape of psychology, two of the most influential modern accounts of why people do what they do have largely run on parallel tracks. Acceptance and Commitment Therapy, or ACT, one of the most widely used third-wave psychotherapies, speaks of deep human “yearnings” that pull people toward meaning, connection, and competence. Self-Determination Theory, or SDT, one of the most heavily researched motivational frameworks in behavioral science, speaks instead of three “basic psychological needs” — autonomy, competence, and relatedness — that function like psychological nutrients. Both ideas claim to describe what humans fundamentally reach for, and both link frustration of those strivings to suffering. Yet until now, nobody had systematically asked whether these two vocabularies are describing the same underlying reality, whether one is nested inside the other, or whether they merely rhyme by coincidence.

A new conceptual analysis by Stefano Mastino and Claudio Mulatti of the University of Trento, published as an open-access article in Current Psychology, takes that question head-on. The authors note that recent years have seen growing empirical attempts to blend the two frameworks, particularly in sport psychology and physical activity promotion, and that prominent figures in both camps have gestured at convergence. Steven Hayes, ACT’s founder, has described euthymia — a state of stable positive mental health — as the balanced satisfaction of both SDT-defined needs and ACT yearnings. Richard Ryan, SDT’s co-founder, has highlighted alignment between ACT principles and SDT findings on autonomous motivation and self-regulation. But as Mastino and Mulatti point out, the theoretical relationship between the two central constructs has remained formally unspecified in the literature. Nobody had clarified whether yearnings and basic needs are equivalent, hierarchically related, or overlapping but distinct.

The paper first lays out what each framework actually claims. In ACT, yearnings are described as deep and universal human longings that orient behavior toward six core domains: belonging, feeling, coherence, orientation, meaning, and competence. These are not treated as pathological in themselves; suffering arises from rigid or avoidant attempts to respond to them. Each yearning is functionally paired with one of ACT’s six psychological flexibility processes. The yearning for belonging is addressed through self-as-context, which loosens attachment to a fixed self-image and opens space for genuine connection. The yearning to feel is met through acceptance, allowing emotions to be experienced openly rather than suppressed. Coherence is handled through cognitive defusion, relating to thoughts as mental events rather than literal truths. Orientation is grounded through present-moment awareness, meaning through values, and competence through committed action.

SDT, by contrast, operates with a far more formalized architecture. Ryan and Deci define basic psychological needs as conditions essential for growth, integrity, and well-being, analogous to biological nutrients — with the crucial difference that they motivate action even without deprivation and can never be fully saturated. The theory specifies explicit criteria a candidate need must meet: its satisfaction must be strongly tied to well-being and its frustration to distress; it must be clearly defined and linked to specific experiences; it must function as an explanatory concept supported by evidence; it must belong to the correct category of variables, acting as an antecedent rather than an outcome; and it must be universal across ages and cultures, with an evolutionary rationale. SDT also distinguishes needs as motivation, which energize behavior at the start of an action sequence, from needs as requirements, whose fulfillment registers as a boost in well-being at the action’s conclusion.

Armed with SDT’s six criteria, the authors then ran the ACT yearnings through a systematic structural comparison. The results are striking in places. On the first criterion — linkage to well-being — both frameworks connect core motivational directions to vitality, though through different explanatory routes: SDT says well-being depends directly on need satisfaction, while ACT emphasizes that psychological flexibility determines whether engaging with yearnings produces vitality or distress. On universality, both ground their constructs in evolutionary reasoning, but SDT embeds needs in a developmental model, whereas ACT does not formally specify that absent yearnings produce developmental failure. On the criterion of clear definition, SDT prescribes specific experiential qualities — autonomy, for instance, is satisfied when behavior feels volitional and self-endorsed — while ACT offers a regulatory rather than prescriptive model, insisting that it is flexible, context-sensitive engagement rather than any fixed behavior that fulfills a yearning.

The most consequential divergence appears on the criterion of empirical status. SDT needs have been operationalized, measured, and tested for decades, with a large literature linking need satisfaction and frustration to health outcomes. ACT yearnings, by contrast, have never been formally defined as distinct motivational constructs, systematically operationalized, or empirically validated in their own right. Research in ACT has overwhelmingly focused on the flexibility processes rather than on the yearnings themselves. The authors conclude that yearnings satisfy the explanatory intent of SDT’s criterion at a functional level while remaining far less empirically formalized. Notably, however, neither framework arranges its motivational constructs hierarchically: SDT rejects Maslow-style sequencing and insists the three needs are interdependent, and ACT likewise designates no yearning as more fundamental than the rest.

The item-by-item comparison then yields a clear map of convergence. The ACT yearning for belonging — the desire to feel recognized, protected, and part of a community — emerges as essentially equivalent to SDT’s need for relatedness, which encompasses being cared for, caring for others, and feeling valued within social groups. The two competence constructs, both rooted in the desire to act effectively and develop skills, substantially coincide; SDT’s version traces back to Robert White’s 1959 account of infant exploration and mastery, while ACT frames it through committed action guided by personal values. The alignment between SDT’s need for autonomy and ACT’s yearning for meaning is significant but only partial. Autonomy concerns how actions are experienced — voluntary and self-endorsed — whereas the yearning for meaning concerns the broader, consciously chosen direction of one’s life. Intriguingly, the authors argue that ACT’s meaning construct effectively integrates autonomy with a separate concept SDT calls “need for meaning,” which SDT deliberately excludes from its basic needs on empirical grounds: the evidence indicates meaning functions as an outcome of satisfying the three basic needs, not as a need in its own right.

Three yearnings resist translation altogether. The yearnings for orientation, coherence, and feeling have no direct conceptual counterpart among SDT’s three needs. But the authors propose an indirect bridge, and it runs through mindfulness. The flexibility processes paired with those yearnings — present-moment awareness, acceptance, and cognitive defusion, together with self-as-context — are core components of mindfulness as conceptualized in ACT. And the SDT literature already links mindfulness to need satisfaction: Steven Brown and Richard Ryan’s classic 2003 research found that mindfulness predicts autonomy, need satisfaction, and self-regulation, while later work showed autonomy mediates the relationship between mindfulness and well-being, and that mindfulness skills support competence in athletes and relatedness in romantic relationships. A doctoral study by Gazla cited in the paper stands out as the only work to date exploring the flexibility–needs connection in detail, reporting strong associations between psychological flexibility and satisfaction of autonomy and competence, more moderate links to relatedness, and mediation analyses suggesting need satisfaction helps explain how flexibility benefits mental health.

From this convergence, the authors advance an integrative proposal: psychological flexibility may function as a regulatory pathway through which engagement with core motivational criteria translates into adaptive functioning. In this reading, ACT processes most closely tied to meaning, competence, and belonging — values, committed action, and self-as-context — act as regulatory mechanisms that facilitate the experiential conditions SDT describes as satisfying autonomy, competence, and relatedness. Several of these processes share features with metacognitive functioning, since they involve observing one’s own thoughts and internal states, raising the possibility that flexibility training could be especially valuable where metacognition is compromised — the authors point to eating disorders, where metacognitive dysfunction is a recognized maintaining factor. The framework also extends across the lifespan: needs for autonomy, competence, and relatedness remain central even in late adulthood and dementia care, and flexibility processes may help older adults sustain need satisfaction. The authors even invoke the COVID-19 lockdowns, which frustrated multiple needs simultaneously, as a case where promoting flexibility could inform psychological preparedness for collective crises.

The authors are careful to flag the limits of their contribution: this is a conceptual rather than empirical analysis, and the proposed links between flexibility processes and need satisfaction remain theoretically grounded but untested within the framework itself. The next step, they argue, is fine-grained longitudinal and mediation research examining how specific ACT processes relate to individual SDT needs, alongside theoretical work to more precisely define and operationalize yearnings so they can be directly compared with established motivational constructs. If that program succeeds, the payoff could be substantial: a unified motivational science in which the clinical machinery of acceptance, defusion, and values-based action is understood not merely as symptom reduction, but as a concrete, trainable route to satisfying the psychological nutrients on which human flourishing demonstrably depends.

Subject of Research: A conceptual comparison of ACT yearnings and Self-Determination Theory basic psychological needs

Article Title: ACT yearnings and SDT basic psychological needs: a conceptual comparison and integrative perspective

Article References: Mastino, S., & Mulatti, C. (2026). ACT yearnings and SDT basic psychological needs: a conceptual comparison and integrative perspective. Current Psychology, 45(18), Article 1532. https://doi.org/10.1007/s12144-026-10093-w

Image Credits: AI Generated

DOI: 10.1007/s12144-026-10093-w

Keywords: Acceptance and Commitment Therapy, Self-Determination Theory, basic psychological needs, yearnings, psychological flexibility, mindfulness, motivation, autonomy, competence, relatedness, well-being, process-based therapy