The term ‘quality’ traverses the depth-psychology corpus along two largely non-communicating axes. The first, and philosophically most sustained, is the Plotinian metaphysical axis, in which quality is rigorously distinguished from substance, activity, and Reason-Principle. For Plotinus, quality is precisely what remains when constitutive differentiation is subtracted from reality: it is a power that adds the property of being quale to substances already existent, never identical with the essence it qualifies. This ontological precision has direct bearing on soul-theory, since psychic qualities inhabiting body occupy an ambiguous threshold between the sensible and the intelligible realms. Rudhyar imports a related but transpositional usage into esoteric psychology, treating quality as the spiritual identity of a living whole — the temporal imprint that individuates a monad at the moment of its inception, making quality the very ground of astrological interpretation. The second axis is methodological and empirical: across the clinical literature in meta-analytic and systematic-review contexts, quality designates the formal rigor of research design — randomization, fidelity, attrition, replication — measurable by validated scales such as the MQRS, PEDro, or the Cochrane Risk of Bias Tool. These two registers rarely converse, yet both treat quality as foundational: one to ontological individuation, the other to epistemic credibility. The tension between quality as intrinsic character and quality as externally assessed standard runs as a largely unthematized fault-line through the corpus.
In opposition to substance, what we call ‘quality’ represents the spiritual identity of the living whole… The quality of the moment and the quality of the wholeness of the whole are identical.
Rudhyar proposes quality as the foundational ontological category in esoteric psychology, equating the quality of a temporal moment with the spiritual identity of any whole that achieves independent existence at that moment.
Quality is a power which adds the property of being qualia to substances already existent. The differences distinguishing substances from each other are called qualities only by analogy; they are, more strictly, Acts and Reason-Principles.
Plotinus defines quality strictly as the power that confers the quale upon pre-existing substances, distinguishing it categorically from the Reason-Principles that constitute essential being.
, The Six Enneads, 270thesis
Where whiteness belongs to the very Reason-Form of the thing it is a constitutive element and not a quality; where it is a superficial appearance it is a quality.
Plotinus draws the pivotal distinction between constitutive differentiation and quality proper, locating quality precisely in the domain of the accidental or superficial, not the essential.
, The Six Enneads, 270thesis
What, then, distinguishes Quality in the Intellectual Realm from that here, if both are Acts? The difference is that these [‘Quality-Activities’] in the Supreme do not indicate the very nature of the Reality.
Plotinus argues that in the Intellectual Realm what appears as quality is in fact pure activity, while quality in the sensible realm arises when reason separates and appropriates a portion of that activity as a distinct characteristic.
, The Six Enneads, 270thesis
Matter, in sum, is necessary to quality and to quantity, and, therefore, to body. It is, thus, no name void of content; we know there is such a base, invisible and without bulk though it be.
Plotinus establishes matter as the necessary substrate for quality’s existence, grounding the metaphysics of quality in a substratum that, though imperceptible, is logically indispensable.
, The Six Enneads, 270supporting
We must examine whether qualities may not prove to be divisible on the principle that some belong to the body and others to the soul. Those of the body would be subdivided according to the senses.
Plotinus proposes a systematic taxonomy of quality, dividing it according to its locus in body or soul and further by sense-modality, activity-type, and moral valence.
, The Six Enneads, 270supporting
Such affections, torn between two worlds by their objects and their abode, we have assigned to Quality, which is indeed not bodily but manifested in body.
Plotinus situates psychic affections that are expressed through bodily manifestation within the category of quality, positioning quality as the mediating term between soul and sensible existence.
, The Six Enneads, 270supporting
The pulp is not merely in touch with water outside it or even in its pores; it is wet through and through so that every particle of its matter is drenched in that quality.
Plotinus uses the physical penetration of matter by moisture to interrogate whether quality can be transmitted through mixing without the material substance itself being present throughout.
, The Six Enneads, 270supporting
If they are privations of qualities, they will themselves be qualities: ‘toothless’ and ‘blind,’ for example, are qualities.
Plotinus extends the category of quality to include privations, demonstrating that the absence of a quality-bearing property is itself a qualitative determination.
, The Six Enneads, 270supporting
When I find Quality bound up with Substance, I regard it as substantial quality: I am not less, but far more, disposed to see in figures or shapes [qualitative] varieties of Quantity.
Plotinus examines the boundary between quality and quantity, arguing that geometric figures are better understood as qualitative varieties of magnitude than as a separate ontological category.
, The Six Enneads, 270supporting
No alteration is possible in respect of essential qualities; the process of alteration that is a pathos is thus alteration in respect of a non-essential quality.
Following Aristotle, Cairns distinguishes essential from non-essential qualities, reserving the concept of alteration — the affective pathos — for changes in the latter, a distinction with direct ethical implications for shame and honour.
, Aidos: The Psychology and Ethics of Honour and Shame in Ancient Greek Literature, 1993supporting
What does endure, however, and constitutes a proper subject of growth, is the ‘peculiarly qualified’ individual, Theon, whose uniquely identifying characteristics must for this purpose be lifelong.
Long and Sedley present the Stoic concept of the ‘peculiarly qualified’ individual as the entity whose defining qualitative profile persists through material flux, making quality central to Stoic theories of personal identity.
, The Hellenistic Philosophers, 1987supporting
The research team created a scoring system to rate each study’s quality… five criteria for rating the quality of each study: (a) appropriate comparison or control groups; (b) random assignment.
Wiersma operationalizes quality as a formal methodological construct in sandplay therapy research, applying APA Division 12 criteria to establish a replicable scoring system for study evaluation.
, A Meta-Analysis of Sandplay Therapy Treatment Outcomes, 2022supporting
Referring only to qualities such as the innate impudence which hardens into shamelessness in the mature.
Cairns observes that Aristotelian natural excellences are best understood as mere dispositions or qualities in a weak sense, becoming genuine virtues only through the habituation that transforms latent capacity into stable character.
, Aidos: The Psychology and Ethics of Honour and Shame in Ancient Greek Literature, 1993aside
One of the novelties of the present study is the analysis performed in regards the effect of exercise on the quality of life of drug-dependent patients.
Giménez-Meseguer deploys quality of life as a clinical outcome variable, demonstrating that exercise interventions produce measurable improvements in this domain among substance-use disorder populations.
Only by formulating a situation or image which, in an actional dramatic manner, will exteriorize the quality of the whole,—and moreover will tend to arouse the experience of that quality in others.
Rudhyar argues that the essential quality of a whole can only be communicated through dramatic symbolic enactment, not through abstract description, grounding his astrological hermeneutics in experiential transmission.