Aristotle analyzed qualities in his
logical work, the
Categories. To him, qualities are
hylomorphically–formal attributes, such as "white" or "grammatical". Categories of
state, such as "shod" and "armed" are also non–
essential qualities
(katà symbebekós).
[3] Aristotle observed: "one and the selfsame substance, while retaining its identity, is yet capable of admitting contrary qualities. The same individual person is at one time white, at another black, at one time warm, at another cold, at one time good, at another bad. This capacity is found nowhere else... it is the peculiar mark of substance that it should be capable of admitting contrary qualities; for it is by itself changing that it does so".
[4]Aristotle described four types of qualitative
opposites:
correlatives, contraries, privatives and
positives.[4] John Locke presented a distinction between primary and secondary qualities in
An Essay Concerning Human Understanding. For Locke, a quality is an
idea of a
sensation or a
perception. Locke further asserts that qualities can be divided in two kinds: primary and secondary qualities.
Primary qualities are
intrinsic to an object—a thing or a person—whereas
secondary qualities are dependent on the
interpretation of the subjective mode and the
context of appearance.
[2] For example, a
shadow is a secondary quality. It requires a certain
lighting to be applied to an object. For another example, consider the
mass of an object.
Weight is a secondary quality since, as a
measurement of gravitational
force, it varies depending on the
distance to, and mass of, very massive objects like the
Earth, as described by
Newton's law. It could be thought that mass is intrinsic to an object, and thus a primary quality. In the context of
relativity, the idea of mass quantifying an amount of
matter requires caution. The
relativistic mass varies for variously traveling observers; then there is the idea of rest mass or
invariant mass (the magnitude of the
energy-momentum 4-vector[5]), basically a system's relativistic mass in its own
rest frame of reference. (Note, however, that Aristotle drew a distinction between qualification and quantification; a thing's quality can vary in degree).
[6] Only an
isolated system's invariant
mass in relativity is the same as observed in variously traveling observers' rest frames, and
conserved in reactions; moreover, a system's heat, including the energy of its massless particles such as photons, contributes to the system's invariant mass (indeed, otherwise even an isolated system's invariant mass would not be conserved in reactions); even a cloud of photons traveling in different directions has, as a whole, a rest frame and a rest energy equivalent to invariant mass.
[7] Thus, to treat rest mass (and by that stroke, rest energy) as an intrinsic quality distinctive of physical matter raises the question of what is to count as physical matter. Little of the invariant mass of a
hadron (for example a
proton or a
neutron) consists in the invariant masses of its component
quarks (in a proton, around 1%) apart from their
gluon particle fields; most of it consists in the
quantum chromodynamics binding energy of the (massless) gluons (see
Quark#Mass).
Philosophy and
common sense tend to see qualities as
related either to
subjective feelings or to
objective facts. The qualities of something
depends on the
criteria being applied to and, from a
neutral point of view, do not determine its value (the
philosophical value as well as
economic value). Subjectively, something might be
good because it is
useful, because it is
beautiful, or simply because it
exists. Determining or finding qualities therefore involves
understanding what is useful, what is beautiful and what exists. Commonly,
quality can mean degree of
excellence, as in, "a quality product" or "work of average quality". It can also refer to a property of something such as "the
addictive quality of
nicotine".
[8] In his book,
Zen and the Art of Motorcycle Maintenance,
Robert M. Pirsig examines concepts of quality in
classical and
romantic, seeking a
Metaphysics of Quality and a
reconciliation of those views in terms of
non-dualistic holism.
Quality is, like
beauty, held in the eye of the beholder, the
subject. Quality is a
subjective phenomenon that is the emergent emotion resulting from the combination of
perception and
expectation. The feeling of high quality occurs when perception exceeds expectation; the feeling of low quality occurs when perception does not meet expectation. When perception and expectation match the sensation is satisfaction which represents neutral quality.
