Aquinas, explains the
nature of metaphysics by distinguishing between two types of intellectual
operations: speculative and practical. In speculative sciences, the intellect
contemplates truth but does not apply it for practical purposes, leading to two
distinct classes of science: speculative science and practical science.
The subject-matter of speculative sciences is that which can be understood to
some extent. Aquinas believes that understanding something is dependent on its
separation from matter and motion. This leads to three divisions of speculative
objects: those dependent on matter and motion both for their being and
understanding; those dependent on matter and motion for their being but not for
their being understood; and those that depend on matter and motion neither for
their being nor for their being understood.
Physical science considers these objects, while mathematics considers them but
not for their being; and metaphysics or theology deals with those that depend
on matter and motion neither for their being nor for their being. Aquinassees
this division of the speculative sciences as exhaustive, as there could be no
fourth speculative science since the subject-matter of such a science would
have to be those things that depend on matter and motion for their being
understood but not for their being.
Aquinas' metaphysics focuses on the third class of speculative objects, which
includes things that depend on matter and motion. These objects are called
positively immaterial, while neutrally immaterial are those that do not depend
on matter and motion but can be found there. The neutrally immaterial can apply
to both material and immaterial things.
Aquinas argues that unaided human reason cannot directly know the positively
immaterial, as they outstrip human intellect's capacity to know. However,
direct knowledge of the positively immaterial requires revelation. Metaphysics
is a purely rational science, not dependent on revelations, and is a study of
the neutrally immaterial aspects of things.
The proper subject-matter of metaphysics is ens commune (common being), which
is the common aspects of being without which a thing could not be. Metaphysics
primarily investigates the nature of essence and existence, which are generally
applicable to all beings. After investigating essence and existence, the
metaphysician must investigate the composition of substance and accident, and
matter and form. The format of Thomistic metaphysics takes a dyadic structure
of descending generality, focusing on essence and existence, substance and
accident, and matter and form.
Aquinas's concept of essence is the definable nature of a thing that exists,
signified by its definition. In finite entities, essence is that which has
existence but is not existence. This is a fundamental metaphysical teaching
that essence and existence are distinct in finite entities. Thomas's most
famous and controversial instance is in De Ente et Essentia [On Being and
Essence] Chapter Four, where he argues for a distinction between a thing's essence
and its existence.
Aquinas takes the notion of universal hylemorphism as absurd, as it contradicts
common philosophers' beliefs and contradicts the potency of immaterial
substances. Instead, Aquinas argues that immaterial substances are composed of essence
and existence, and it is the essence of the thing that accounts for the
potentiality of creatures and distinguishes them from God.
Acquinas's argumentation for the distinction between essence and existence
unfolds on three stages, with some commentators arguing that he intended and
established the real distinction therein. Some argue that it is merely a
logical distinction, while others focus on the distinction between the act of
understanding a thing's essence and the act of knowing its existence.
Aquinas argues that a being whose essence is its existence would be unique and
exist in a single absolute reality. This is evident from the way things can be
multiplied, which can be in three ways: as a genus multiplied into its species,
as a species multiplied into its individuals through being composed with
matter, or as a thing is absolute and shared in by many particular things. Aquinasargues
that a being whose essence is its existence cannot be multiplied in either of
these ways, as it would not be subsistent but would be subsistent if it exists
in virtue of what it is.
John Wippel argues that this is the decisive stage in establishing that essence
and existence are really distinct. He argues that there cannot be more than one
being whose essence is its existence, so there could not be many such beings in
reality. Joseph Owens, on the other hand, argues that we cannot establish the
real distinction until we have established that there is something whose
essence is its existence. He argues that Aquinasestablishes the real
distinction by comparing the existence of a being whose essence is its
existence with the existence of finite entities, demonstrating that essence and
existence are really distinct.
Aquinas’ metaphysical teachings on essence and existence are based on the idea
that essence and existence are distinct concepts. He concludes that in
immaterial substances, essence is related to existence as potency to act, which
means that what receives existence stands in potency to the existence it receives.
All things receive existence from the being whose essence is its existence, and
the existence that any one finite thing possesses is an act of existence that
actuates a corresponding potency: the essence.
Aquinas’ fundamental metaphysical teachings emphasize the importance of
existence being efficiently caused in the essence/existence composite. He
defines participation as taking part in something, which can happen in three
ways: receiving universally relevant information, participating in accidents, or
participating in its cause. Participation limits the nature of the thing in
which it participates, as the participant will not possess the nature of the
thing in which it participates in any total fashion but only in partial
fashion.
Essences exist, but they do not exist essentially, participating in their acts
of existence. Insofar as an essence participates in its act of existence, the
essence limits that act of existence to the nature of the essence whose act it
is. The act of existence is thus limited and individuated to the essence whose
act it is, as the essence merely participates in and thereby limits the act of
existence that it possesses.
Aquinas's metaphysical category of substance is primarily comprised of
substances, which are essence/existence composites. Substances are basic
entities that exist per se but are not identical with existence. The paradigm
instances of substances are medium-sized objects like horses, cats, trees, and
humans.
Accidents are incidental to substances and can only exist as part of some
substance. In Aquinas's metaphysical framework, substances can be both material
(cats, dogs, humans) and immaterial (angels). Material substances are
composites of matter and form, and their parts cannot exist independently.
While parts of a substance are parts of a substance, they cannot themselves be
substances. However, the elements out of which a substance is made can subsist
beyond the dissolution of the substance. When the substance dissolves, the
elements remain as independent substances in their own right.
In contemporary terms, atoms are substances in themselves before they form
bodily substances, but when united in a certain form, they become substances in
themselves. When the cat or dog or human perishes, its flesh and bones perish,
but its atoms regain their substantial nature and remain as substances in
themselves.
In conclusion, Aquinas's metaphysical framework focuses on the existence of
substances and their relationships with their constituent parts. While parts of
a substance cannot exist independently, they can be considered as substances in
themselves when the substance decomposes.
Matter and form are fundamental concepts in physics, with matter being the
substance from which a thing is made and form signified by its organization. A
common example is a marble statue, where the marble is the material and the
shape signifies the form. Form is the principle of potency in a thing, meaning
it can be potentially an indefinite number of forms.
There are certain levels of matter/form composition, with the marble being the
form and the marble being the matter. Prime matter, on the other hand, is the
ultimate subject of form and indefinable. It is neither a substance nor any
other categories of being, as it does not exist except as potency.
Matter can be considered in two senses: designated and undesignated. Designated
matter is the type of matter to which one can point and make use, while
undesignated matter is the abstracted notion of matter. Designated matter
individuates some form, ensuring individuals of the same form (man).
Form can be substantial or accidental, with substantial form always informing
prime matter and bringing a new substance into existence. Accidental form
informs an already existing substance, modifying some substance. There can only
be one substantial form of a thing, as any other form that may accrue to a
thing is posterior to it and informs an already constituted substance.
