A number of
popes and Church law direct that the method, doctrines, and
principles of St. Thomas Aquinas be taught in schools and
especially in seminaries. After a special statement on this matter
by Pope St. Pius X (motu proprio, Doctoris Angelici
on June 29, 1914) a number of philosophy professors met, drew up a
list of the principles and major tenets of St. Thomas, and
submitted the list to the Sacred Congregation of Studies. On July
27, 1914, this Congregation declared that in their judgment this
list contained the principles and major tenets of St. Thomas'
philosophy, especially in metaphysics.
Congregation itself, in 1916, declared that these were safe,
directive norms. Though the list often does not give the exact
wording of St. Thomas, it is sure that the ideas are St. Thomas'.
Hence, if St. Thomas is the safe, approved teacher of philosophy
for Catholics, his ideas must be safe and approved norms. A
philosopher who intellectually accepts all of these theses is
named a Thomist; and this meaning of the term Thomist is about the
only definite meaning that can be assigned to it. The theses are
given here for convenient reference.
professors to bear well in mind that they cannot set aside St.
Thomas, especially in metaphysical questions, without grave
disadvantage. St. Pius X, Pascendi Dominici Gregis,
September 8, 1907
These 24 propositions are a concise guide of the whole philosophy
and can be divided as follows:
Cosmology (Th. 8–12)
Psychology (Th. 13–21)
Potency and Act
divide being in such a way that whatever is, is either pure act,
or of necessity it is composed of potency and act as primary and
Since act is perfection, it is not limited except through a
potency which itself is a capacity for perfection. Hence in any
order in which an act is pure act, it will only exist, in that
order, as a unique and unlimited act. But whenever it is finite
and manifold, it has entered into a true composition with potency.
Consequently, the one God, unique and simple, alone subsists in
absolute being. All other things that participate in being have a
nature whereby their being is restricted; they are constituted of
essence and being, as really distinct principles.
4. A thing is called a being
because of being (esse). God and creature are not called
beings univocally, nor wholly equivocally, but analogically, by an
analogy both of attribution and of proportionality.
5. In every creature there is also a real composition of
the subsisting subject and of added secondary forms, i.e.,
accidental forms. Such composition cannot be understood unless
being is really received in an essence distinct from it.
Besides the absolute accidents there is also the relative
accident, relation. Although by reason of its own character
relation does not signify anything inhering in another, it
nevertheless often has a cause in things, and hence a real entity
distinct from the subject.
A spiritual creature is wholly simple in its essence. Yet there is
still a twofold composition in the spiritual creature, namely,
that of the essence with being, and that of the substance with
However, the corporeal creature is composed of act and potency
even in its very essence. These act and potency in the order of
essence are designated by the names form and matter respectively.
matter nor the form have being of themselves, nor are they
produced or corrupted of themselves, nor are they included in any
category otherwise than reductively, as substantial principles.
Although extension in quantitative parts follows upon a corporeal
nature, nevertheless it is not the same for a body to be a
substance and for it to be quantified. For of itself substance is
indivisible, not indeed as a point is indivisible, but as that
which falls outside the order of dimensions is indivisible. But
quantity, which gives the substance extension, really differs from
the substance and is truly an accident.
The principle of individuation, i.e., of numerical distinction of
one individual from another with the same specific nature, is
matter designated by quantity. Thus in pure spirits there cannot
be more than individual in the same specific nature.
By virtue of a body's quantity itself, the body is
circumscriptively in a place, and in one place alone
circumscriptively, no matter what power might be brought to
Bodies are divided into two groups; for some are living and others
are devoid of life. In the case of the living things, in order
that there be in the same subject an essentially moving part and
an essentially moved part, the substantial form, which is
designated by the name soul, requires an organic disposition, i.e.,
Souls in the vegetative and sensitive orders cannot subsist of
themselves, nor are they produced of themselves. Rather, they are
no more than principles whereby the living thing exists and lives;
and since they are wholly dependent upon matter, they are
incidentally corrupted through the corruption of the composite.
On the other hand, the human soul subsists of itself. When it can
be infused into a sufficiently disposed subject, it is created by
God. By its very nature, it is incorruptible and immortal.
This rational soul is united to the body in such a manner that it
is the only substantial form of the body. By virtue of his soul a
man is a man, an animal, a living thing, a body, a substance and a
being. Therefore the soul gives man every essential degree of
perfection; moreover, it gives the body a share in the act of
being whereby it itself exists.
From the human soul there naturally issue forth powers pertaining
to two orders, the organic and the non-organic. The organic
powers, among which are the senses, have the composite as their
subject. The non-organic powers have the soul alone as their
subject. Hence, the intellect is a power intrinsically independent
of any bodily organ.
Intellectuality necessarily follows upon immateriality, and
furthermore, in such manner that the father the distance from
matter, the higher the degree of intellectuality. Any being is the
adequate object of understanding in general. But in the present
state of union of soul and body, quiddities abstracted from the
material conditions of individuality are the proper object of the
Therefore, we receive knowledge from sensible things. But since
sensible things are not actually intelligible, in addition to the
intellect, which formally understands, an active power must be
acknowledged in the soul, which power abstracts intelligible
likeness or species from sense images in the imagination.
Through these intelligible likenesses or species we directly know
universals, i.e., the natures of things. We attain to singulars by
our senses, and also by our intellect, when it beholds the sense
images. But we ascend to knowledge of spiritual things by analogy.
The will does not precede the intellect but follows upon it. The
will necessarily desires that which is presented to it as a good
in every respect satisfying the appetite. But it freely chooses
among the many goods that are presented to it as desirable
according to a changeable judgment or evaluation. Consequently,
the choice follows the final practical judgment. But the will is
the cause of it being the final one.
We do not perceive by an immediate intuition that God exists, nor
do we prove it a priori. But we do prove it a posteriori,
from the things that have been created, following an argument from
the effects to the cause: namely, from things which are moved and
cannot be the adequate source of their motion, to a first unmoved
mover; from the production of the things in this world by causes
subordinated to one another, to a first uncaused cause; from
corruptible things which equally might be or not be, to an
absolutely necessary being; from things which more or less are,
live, and understand, according to degrees of being, living and
understanding, to that which is maximally understanding, maximally
living and maximally a being; finally, from the order of all
things, to a separated intellect which has ordered and organized
things, and directs them to their end.
The metaphysical motion of the Divine Essence is correctly
expressed by saying that it is identified with the exercised
actuality of its won being, or that it is subsistent being itself.
And this is the reason for its infinite and unlimited
By reason of the very purity of His being, God is distinguished
from all finite beings. Hence it follows, in the first place, that
the world could only have come from God by creation; secondly,
that not even by way of a miracle can any finite nature be given
creative power, which of itself directly attains the very being of
any being; and finally, that no created agent can in any way
influence the being of any effect unless it has itself been moved
by the first Cause.
publishing the Canon Law, Pope Benedict XV ordered the method,
doctrines and principles of St. Thomas to be followed (Code, can.
1366, § 2) and gave as reference the decree of the Sacred
Congregation approving the 24 Thesis.
is the source of the list of theses. It evaluates them as a good
statement of the principles and major views of St. Thomas'
philosophy. The same Acta, VII (1916), 15758,
refers to them as safe, directive norms.
1 St Th. Ia. Q.77, a.1; Metaph.
VII, 1 and IX, 1 and 9
2 St Th. Ia. Q.7, a.1-2; Cont. Gent. I, c.43; I Sent. Dist.43,
3 St Th. Ia. Q.50, a.2, ad 3; Cont. Gent. I, c.38,52,53,54; I
Sent. Dist.19, Q.2, a.2 ; De Ent. et Ess. c.5; De Spir. Creat.
a.1; De Verit. Q.27, a.1, ad 8
4 St Th. Ia. Q.13, a.5; Cont. Gent. I, c.32,33,34; De Pot.
5 St Th. Ia. Q.3, a.6; Cont. Gent. I, c.23; Cont. Gent. II,
c.52; De Ent. et Ess. c.5
6 St Th. Ia. Q.28, mainly a.1
7 St Th. Ia. Q.50 and ff; De Spirit. Creat. a.1
8 St Th. De Spirit. Creat. a.1
9 St Th. Ia. Q.45, a.4; De Pot. Q.3, a.5, ad 3 ;
10 St Th. Cont. Gent. IV, c.65; I Sent. Dist. 37, Q.2, a.1, ad
3; II Sent. Dist. 30, Q.2, a.1
11 St Th. Cont. Gent. II, c.92-93; Ia. Q.50, a.4; De Ent. et
12 St Th. IIIa. Q.75; IV Sent. Dist. 10, a.3
13 St Th. Ia. Q.18, a.1-2 and Q.75, a.1; Cont. Gent.
I, c.97; De Anima
14 St Th. Ia. Q.75, a.3 and Q.90, a.2; Cont. Gent. II, c.80
15 St Th. Ia. Q.75, a.2 and Q.90 and 118; Cont. Gent. II, c.83
and ff.; De Pot. Q.3, a.2; De Anim. a.14
16 St Th. Ia. Q.76; Cont. Gent. II, c.56, 68-71; De Anim. a.1;
De Spirit. Creat. a.3
17 St Th. Ia. Q.77-79; Cont. Gent. II, c.72; De Anim. a.12 and
ff.; De Spirit. Creat. a.11
18 St Th. Ia. Q.14, a.1 and Q.74, a.7 and Q.89, a.1-2; Cont.
Gent. I, c.59 and 72, and IV, c.2
19 St Th. Ia. Q.79, a.3-4 and Q.85, a.6-7; Cont. Gent. II,
c.76 and ff.; De Spirit. Creat. a.10
20 St Th. Ia. Q.85-88
21] St Th. Ia. Q.82-83; Cont. Gent. II, c.72 and ff.; De Verit.
Q.22, a.5; De Malo Q.11
22 St Th. Ia. Q.2; Cont. Gent. I, c.12 and 31 and III c.10-11;
De Verit. Q.1 and 10; De Pot. Q.4 and 7
23 St Th. Ia. Q.4 , a.2 and Q.13, a.11; I Sent. Dist. 8, Q.1
24 St Th. Ia. Q.44-45 and 105; Cont. Gent. II, c.6-15 and III
c.66-69 and IV c.44; De Pot. mainly Q.3, a.7