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Overview

Thomas Aquinas held and practiced the principle that truth is to be accepted no matter where it is found. His doctrines drew from Greek, Roman, Islamic and Jewish philosophers. Specifically, he was a realist (i.e. unlike skeptics, he believed that the world can be known as it is). He often affirmed Aristotle's views with independent arguments, and largely followed Aristotelian terminology and metaphysics. He wrote comprehensive commentaries on Aristotle, and respectfully referred to him simply as "the Philosopher".[4]

He also adhered to some neoplatonic principles, for example that "it is absolutely true that there is first something which is essentially being and essentially good, which we call God, ... [and that] everything can be called good and a being, inasmuch as it participates in it by way of a certain assimilation..."[5]

24 Thomistic Theses

With the decree Postquam sanctissimus of 27 July 1914,[6] Pope Pius X declared that 24 theses formulated by "teachers from various institutions ... clearly contain the principles and more important thoughts" of Aquinas. Principal contributors to the Church's official statement of the "24 Theses" of Thomism include Dominican philosopher and theologian Edouard Hugon of the Pontifical University of Saint Thomas Aquinas, Angelicum and Jesuit philosopher theologian Guido Mattiussi of the Pontifical Gregorian University.

Ontology

  1. 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 intrinsic principles.
  2. 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.
  3. 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 "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.
  6. 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.
  7. 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 accidents.
  8. 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.

Cosmology

  1. Neither the 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.
  2. 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

    Thomism is the philosophical school that arose as a legacy of the work and thought of Thomas Aquinas (1225–1274), philosopher, theologian, and Doctor of the Church. In philosophy, Aquinas' disputed questions and commentaries on Aristotle are perhaps his best-known works.

    In theology, his Summa Theologica is amongst the most influential documents in medieval theology and continues to be the central point of reference for the philosophy and theology of the Catholic Church. In the 1914 encyclical Doctoris Angelici[1] Pope Pius X cautioned that the teachings of the Church cannot be understood without the basic philosophical underpinnings of Aquinas' major theses:

    The capital theses in the philosophy of St. Thomas are not to be placed in the category of opinions capable of being debated one way or another, but are to be considered

    In theology, his Summa Theologica is amongst the most influential documents in medieval theology and continues to be the central point of reference for the philosophy and theology of the Catholic Church. In the 1914 encyclical Doctoris Angelici[1] Pope Pius X cautioned that the teachings of the Church cannot be understood without the basic philosophical underpinnings of Aquinas' major theses:

    The capital theses in the philosophy of St. Thomas are not to be placed in the category of opinions capable of being debated one way or another, but are to be considered as the foundations upon which the whole science of natural and divine things is based; if such principles are once removed or in any way impaired, it must necessarily follow that students of the sacred sciences will ultimately fail to perceive so much as the meaning of the words in which the dogmas of divine revelation are proposed by the magistracy of the Church.[2]

    The Second Vatican Council described Aquinas' system as the "Perennial Philosophy."[3]

    Thomas Aquinas held and practiced the principle that truth is to be accepted no matter where it is found. His doctrines drew from Greek, Roman, Islamic and Jewish philosophers. Specifically, he was a realist (i.e. unlike skeptics, he believed that the world can be known as it is). He often affirmed Aristotle's views with independent arguments, and largely followed Aristotelian terminology and metaphysics. He wrote comprehensive commentaries on Aristotle, and respectfully referred to him simply as "the Philosopher".[4]

    He also adhered to some neoplatonic principles, for example that "it is absolutely true that there is first something which is essentially being and essentially good, which we call God, ... [and that] everything can be called good and a being, inasmuch as it participates in it by way of a certain assimilation..."[5]

    24 Thomistic Theses

    With the decree Postquam sanctissimus of 27 July 1914,[6] Pope Pius X declared that 24 theses formulated by "teachers from various institutions ... clearly contain the principles and more important thoughts" of Aquinas. Principal contributors to the Church's official statement of the "24 Theses" of Thomism include Dominican philosopher and theologian Edouard Hugon of the Pontifical University of Saint Thomas Aquinas, Angelicum and Jesuit philosopher theologian Guido Mattiussi of the Pontifical Gregorian University.

    Ontology

    1. 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 intrinsic principles.
    2. 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.
    3. 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 "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.
    6. 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.
    7. 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 accidents.
    8. 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.

    Cosmology

    1. Neither the 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.
    2. 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.
    3. 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 one individual in the same specific nature.
    4. 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 bear.
    5. 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. heterogeneous parts.

    Psychology

    1. 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.
    2. 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.
    3. 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.
    4. 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.
    5. Intellectuality necessarily follows upon immateriality, and furthermore, in such manner that the further 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, quantities abstracted from the material conditions of individuality are the proper object of the human intellect.
    6. 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.
    7. 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.
    8. 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.

    God

    1. 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, i.e., 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.
    2. The metaphysical motion of the Divine Essence is correctly expressed by saying that it is identified with the exercised actuality of its own being, or that it is subsistent being itself. And this is the reason for its infinite and unlimited perfection.
    3. 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.

    Metaphysics

    Aquinas says that the fundamental axioms of ontology are the principle of non-contradiction and the principle of causality. Therefore, any being that does not contradict these two laws could theoretically exist,[7] even if said being were incorporeal.[8]

    Predication

    Aquinas noted three forms of descriptive language when predicating: univocal, analogical, and equivocal.[9]

    • Univocality is the use of a descriptor in the same sense when applied to two objects or groups of objects. For instance, when the word "milk" is applied both to milk produced by cows and by any other female mammal.
    • Analogy occurs when a descriptor changes some but not all of its meaning. For example, the word "healthy" is analogical in that it applies both to a healthy person or animal (those that enjoy of good health) and to some food or drink (if it is good for the health).
    • Equivocation is the complete change in meaning of the descriptor and is an informal fallacy. For example, when the word "bank" is applied to river banks and financial banks, modern philosophers talk of ambiguity.

    Further, the usage of "definition" that Aquinas gives is the genus of the being, plus a difference that sets it apart from the genus itself. For instance, the Aristotelian definition of "man" is "rational animal"; its genus being animal, and what sets apart man from other animals is his rationality.[10]

    Being

    [E]xistence is twofold: one is essential existence or the substantial existence of a thing, for example man exists, and this is existence simpliciter. The other is neoplatonic principles, for example that "it is absolutely true that there is first something which is essentially being and essentially good, which we call God, ... [and that] everything can be called good and a being, inasmuch as it participates in it by way of a certain assimilation..."[5]

    With the decree Postquam sanctissimus of 27 July 1914,[6] Pope Pius X declared that 24 theses formulated by "teachers from various institutions ... clearly contain the principles and more important thoughts" of Aquinas. Principal contributors to the Church's official statement of the "24 Theses" of Thomism include Dominican philosopher and theologian Edouard Hugon of the Pontifical University of Saint Thomas Aquinas, Angelicum and Jesuit philosopher theologian Guido Mattiussi of the Pontifical Gregorian University.

    Ontology

    axioms of ontology are the principle of non-contradiction and the principle of causality. Therefore, any being that does not contradict these two laws could theoretically exist,[7] even if said being were incorporeal.[8]

    Predication

    Aquinas noted three forms of descriptive language when predicating: univocal, analogical, and equivocal.[9]

    • Univocality is the use of a descriptor in the same sense when applied to two objects or groups of objects. For instance, when the word "milk" is applied both to milk produced by cows and by any other female mammal.
    • Analogy occurs when a descriptor changes some but not all of its meaning. For example, the word "healthy" is analogical in that it applies both to a healthy person or animal (those that enjoy of good health) and to some food or drink (if it is good for the health).
    • Equivocation is the complete change in meaning of the descriptor and is an informal fallacy. For example, when the word "bank" is applied to river banks and financial banks, modern philosophers talk of ambiguity.

    Further, the usage of "definition" that Aquinas gives is the genus of the being, plus a difference that sets it apart from the genus itself. For instance, the Aristotelian definition of "man" is "rational animal"; its genus being animal, and what sets apart man from other animals is his rationality.[10]

    Being

    [E]xistence is twofold: one is essential existence or the substantial existence of a thing, for example man exists, and this is existence simpliciter. The other is accidental existence, for example man is white, and this is existence secundum quid.

    In Thomist philosophy, the definition of a being is "that which is," which is composed of two parts: "which" refers to its quiddity (literally "whatness"), and "is" refers to its esse (the Latin infinitive verb "to be").[11] "Quiddity" is synonymous with essence, form and nature; whereas "esse" refers to the principle of the being's existence. In other words, a being is "an essence that exists."[12]

    Being is divided in two ways: that which is in itself (substances), and that which is in another (accidents). Substances are things which exist per se or in their own right. Accidents are qualities that apply to other things, such as shape or color: "[A]ccidents must include in their definition a subject which is outside their genus."[13] Because they only exist in other things, Aquinas holds that metaphysics is primarily the study of substances, as they are the primary mode of being.[14]

    The Catholic Encyclopedia pinpoints Aquinas' definition of quiddity as "that which is expressed by its definition."[15] The quiddity or form of a thing is what makes the object what it is: "[T]hrough the form, which is the actuality of matter, matter becomes something actual and something individual,"[16] and also, "the form causes matter to be."[17] Thus, it consists of two parts: "prime matter" (matter without form),[18] and substantial form, which is what causes a substance to have its characteristics. For instance, an animal can be said to be a being whose matter is its body, and whose soul[19] is its substantial form.[20][21] Together, these consist of its quiddity/essence.

    All real things have the transcendental properties of being: oneness, truth, goodness (that is, all things have a final cause and therefore a purpose), etc.[22]

    Causality

    Aristotle categorized causality into four subsets in the Metaphysics, which is an integral part of Thomism:

    "In one sense the term cause means (a) that from which, as something intrinsic, a thing comes to be, as the bronze of a statue and the silver of a goblet, and the genera of these. In another sense it means (b) the form and pattern of a thing, i.e., the intelligible expression of the quiddity and its genera (for example, the ratio of 2:1 and number in general are the cause of an octave chord) and the parts which are included in the intelligible expression. Again, (c) that from which the first beginning of change or of rest comes is a cause; for example, an adviser is a cause, and a father is the cause of a child, and in general a maker is a cause of the thing made, and a changer a cause of the thing changed. Further, a thing is a cause (d) inasmuch as it is an end, i.e., that for the sake of which something is done; for example, health is the cause of walking. For if we are asked why someone took a walk, we answer, "in order to be healthy"; and in saying this we think we have given the cause. And whatever occurs on the way to the end under the motion of something else is also a cause. For example, reducing, purging, drugs and instruments are causes of health; for all of these exist for the sake of the end, although they differ from each other inasmuch as some are instruments and others are processes."

    • (a) refers to the material cause, what a being's matter consists of (if applicable).
    • (b) refers to the formal cause, what a being's essence is.
    • (c) refers to the efficient cause, what brings about the beginning of, or change to, a being.
    • (d) refers to the final cau

      Aquinas noted three forms of descriptive language when predicating: univocal, analogical, and equivocal.[9]

      • Univocality is the use of a descriptor in the same sense when applied to two objects or groups of objects. For instance, when the word "milk" is applied both to milk produced by cows and by any other female mammal.
      • Analogy occurs when a descriptor changes some but not all of

        Further, the usage of "definition" that Aquinas gives is the genus of the being, plus a difference that sets it apart from the genus itself. For instance, the Aristotelian definition of "man" is "rational animal"; its genus being animal, and what sets apart man from other animals is his rationality.[10]

        Being

        [E]xistence is twofold: one is essential existence or the substantial existence of a thing, for example man exists, and this is existence simpliciter. The other is substantial existence of a thing, for example man exists, and this is existence simpliciter. The other is accidental existence, for example man is white, and this is existence secundum quid.

        In Thomist philosophy, the definition of a being is "that which is," which is composed of two parts: "which" refers to its quiddity (literally "whatness"), and "is" refers to its esse (the Latin being is "that which is," which is composed of two parts: "which" refers to its quiddity (literally "whatness"), and "is" refers to its esse (the Latin infinitive verb "to be").[11] "Quiddity" is synonymous with essence, form and nature; whereas "esse" refers to the principle of the being's existence. In other words, a being is "an essence that exists."[12]

        Being is divided in two ways: that which is in itself (substances), and that which is in another (substances), and that which is in another (accidents). Substances are things which exist per se or in their own right. Accidents are qualities that apply to other things, such as shape or color: "[A]ccidents must include in their definition a subject which is outside their genus."[13] Because they only exist in other things, Aquinas holds that metaphysics is primarily the study of substances, as they are the primary mode of being.[14]

        The Catholic Encyclopedia pinpoints Aquinas' definition of quiddity as "that which is expressed by its definition."[15] The quiddity or form of a thing is what makes the object what it is: "[T]hrough the form, which is the actuality of matter, matter becomes something actual and something individual,"[16] and also, "the form causes matter to be."[17] Thus, it consists of two parts: "prime matter" (matter without form),[18] and substantial form, which is what causes a substance to have its characteristics. For instance, an animal can be said to be a being whose matter is its body, and whose soul[19] is its substantial form.[20][21] Together, these consist of its quiddity/essence.

        All real things have the transcendental properties of being: oneness, truth, goodness (that is, all things have a final cause and therefore a purpose), etc.[22]

        Aristotle categorized causality into four subsets in the Metaphysics, which is an integral part of Thomism:

        "In one sense the term cause means (a) that from which, as something intrinsic, a thing comes to be, as the bronze of a statue and the silver of a goblet, and the genera of these. I

        "In one sense the term cause means (a) that from which, as something intrinsic, a thing comes to be, as the bronze of a statue and the silver of a goblet, and the genera of these. In another sense it means (b) the form and pattern of a thing, i.e., the intelligible expression of the quiddity and its genera (for example, the ratio of 2:1 and number in general are the cause of an octave chord) and the parts which are included in the intelligible expression. Again, (c) that from which the first beginning of change or of rest comes is a cause; for example, an adviser is a cause, and a father is the cause of a child, and in general a maker is a cause of the thing made, and a changer a cause of the thing changed. Further, a thing is a cause (d) inasmuch as it is an end, i.e., that for the sake of which something is done; for example, health is the cause of walking. For if we are asked why someone took a walk, we answer, "in order to be healthy"; and in saying this we think we have given the cause. And whatever occurs on the way to the end under the motion of something else is also a cause. For example, reducing, purging, drugs and instruments are causes of health; for all of these exist for the sake of the end, although they differ from each other inasmuch as some are instruments and others are processes."

        — ancient Greeks, who thought that an infinite regress of causality is possible (and thus held that the universe is uncaused), Aquinas argues that an infinite chain never accomplishes its objective and is thus impossible.[23] Hence, a first cause is necessary for the existence of anything to be possible. Further, the First Cause must continuously be in action (similar to how there must always be a first chain in a chain link), otherwise the series collapses:[24]

        The Philosopher says (Metaph. ii, 2) that "to suppose a thing to be indefinite is to deny that it is good." But the good is that which has the nature of an end. Therefore it is contrary to the nature of an end to proceed indefinitely. Therefore it is necessary to fix one last end.

        — The Philosopher says (Metaph. ii, 2) that "to suppose a thing to be indefinite is to deny that it is good." But the good is that which has the nature of an end. Therefore it is contrary to the nature of an end to proceed indefinitely. Therefore it is necessary to fix one last end.

        — [23][25][26][27] because an infinite regress is impossible.[28]

        However, the First Cause does not necessarily have to be temporally the first. Thus, the question of whether or not the universe can be imagined as eternal was fiercely debated in the Middle Ages. The University of Paris's condemnation of 1270 denounced the belief that the world is eternal. Aquinas' intellectual rival, Bonaventure, held that the temporality of the universe is demonstrable by reason.[29][30] Aquinas' position was that the temporality of the world is an article of faith, and not demonstrable by reason; though one could reasonably conclude either that the universe is temporal or eternal.[31][32]

        As per the Nicomachean Ethics of Aristotle,[33] Aquinas defines "the good" as what all things strive for. E.g., a cutting knife is said to be good if it is effective at its function, cutting. As all things have a function/final cause, all real things are good. Consequently, evil is nothing but privatio boni, or "lack of good", as Augustine of Hippo defined it.[34]

        Dionysius says (Div. Nom. iv), 'Evil is neither a being nor a good.' I answer that, one opposite

        Dionysius says (Div. Nom. iv), 'Evil is neither a being nor a good.' I answer that, one opposite is known through the other, as darkness is known through light. Hence also what evil is must be known from the nature of good. Now, we have said above that good is everything appetible; and thus, since every nature desires its own being and its own perfection, it must be said also that the being and the perfection of any nature is good. Hence it cannot be that evil signifies being, or any form or nature. Therefore it must be that by the name of evil is signified the absence of good. And this is what is meant by saying that 'evil is neither a being nor a good.' For since being, as such, is good, the absence of one implies the absence of the other.

        — [35]

        As God is the ultimate end of all things,[36] God is by essence goodness itself.As God is the ultimate end of all things,[36] God is by essence goodness itself.[37] Furthermore, since love is "to wish the good of another,"[38] true love in Thomism is to lead another to God. Hence why John the Evangelist says, "Whoever is without love does not know God, for God is love."[39][40]

        Thomas Aquinas holds that the existence of God can be demonstrated by reason,[41] a view that is taught by the Catholic Church.[42] The quinque viae (Latin: five ways) found in the Summa Theologica (I, Q.2, art.3) are five possible ways of demonstrating the existence of God,[43] which today are categorized as:

        1. Argumentum ex motu, or the argument of the unmoved mover;
        2. Argumentum ex ratione causae efficientis, or the argument of the first cause;
        3. Argumentum ex contingentia, or the argument from contingency;
        4. Argumentum ex

        Despite this, Aquinas also thought that sacred mysteries such as the Trinity could only be obtained through revelation; though these truths cannot contradict reason:

        The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected. Nevertheless, there is nothing to prevent a man, who cannot grasp a proof, accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated.

        — SummaThe existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected. Nevertheless, there is nothing to prevent a man, who cannot grasp a proof, accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated.

        — problem of evil by saying that God allows evil to exist that good may come of it,[44] (for goodness done out of free will is superior than goodness done from biological imperative) but does not personally cause evil Himself.[45]

        See also Reality: A Synthesis of Thomistic ThoughtSee also Reality: A Synthesis of Thomistic Thought: Chapter 7: The Proofs Of God's Existence by Reginald Garrigou-Lagrange.

        Aquinas articulated and defended, both as a philosopher and a theologian, the orthodox Christian view of God. God is the sole being whose existence is the same as His essence: "what subsists in God is His existence."[46] (Hence why God names himself "I Am that I Am" in Exodus 3:14.[47]) Consequently, God cannot be a body (that is, He cannot be composed of matter),[48] He cannot have any accidents,[49] and He must be simple (that is, not separated into parts; the Trinity is one substance in three persons).[50] Further, He is goodness itself,[37] perfect,[51] infinite,[52] omnipotent,[53] omniscient,[54] happiness itself,[55] knowledge itself,[56] love itself,[40] omnipresent,[57] immutable,[58] and eternal.[59] Summing up these properties, Aquinas offers the term actus purus (Latin: "pure actuality").

        Aquinas held that not only does God have knowledge of everything,[54] but that God has "the most perfect knowledge," and that it is also true to say

        Aquinas held that not only does God have knowledge of everything,[54] but that God has "the most perfect knowledge," and that it is also true to say that God "is" His understanding.[56]

        Aquinas also understands God as the transcendent cause of the universe, the "first Cause of all things, exceeding all things caused by Him," the source of all creaturely being and the cause of every other cause.[60] Consequently, God's causality is not like the causality of any other causes (all other causes are "secondary causes"), because He is the transcendent source of all being, causing and sustaining every other existing thing at every instant. Consequently, God's causality is never in competition with the causality of creatures; rather, God even causes some things through the causality of creatures.[61]

        Aquinas was an advocate of the "analogical way", which says that because God is infinite, people can only speak of God by analogy, for some of the aspects of the divine nature are hidden (Deus absconditus) and others revealed (Deus revelatus) to finite human minds. Thomist philosophy holds that we can know about God through his creation (general revelation), but only in an analogous manner.[62] For instance, we can speak of God's goodness only by understanding that goodness as applied to humans is similar to, but not identical with, the goodness of God. Further, he argues that sacred scripture employs figurative language: "Now it is natural to man to attain to intellectual truths through sensible objects, because all our knowledge originates from sense. Hence in Holy Writ, spiritual truths are fittingly taught under the likeness of material things."[63]

        In order to demonstrate God's creative power, Aquinas says: "If a being participates, to a certain degree, in an 'accident,' this accidental property must have been communicated to it by a cause which possesses it essentially. Thus iron becomes incandescent by the action of fire. Now, God is His own power which subsists by itself. The being which subsists by itself is necessarily one."[23]

        In addition to agreeing with the Aristotelian definition of man as "the rational animal,"[10] Aquinas also held various other beliefs about the substance of man. For instance, as the essence (nature) of all men are the same,[64] and the definition of being is "an essence that exists,"[12] humans that are real therefore only differ by their specific qualities. More generally speaking, all beings of the same genus have the same essence, and so long as they exist, only differ by accidents and substantial form.[65]

        Soul

        Thomists define the soul as the substantial form of living beings.[66] Thus, plants have "vegetative souls," animals have "sensitive souls,"[19] while human beings alone have "intellectual" – rational and immortal – souls.[67]

        For Aristotle, the soul is one, but endowed with five groups of faculties (dunámeis): (1) the "vegetative" faculty (threptikón), concerned with the maintenance and development of organic life; (2) the appetite (oretikón), or the tendency to any good; (3) the faculty of s

        Thomists define the soul as the substantial form of living beings.[66] Thus, plants have "vegetative souls," animals have "sensitive souls,"[19] while human beings alone have "intellectual" – rational and immortal – souls.[67]

        For Aristotle, the soul is one, but endowed with five groups of faculties (dunámeis): (1) the "vegetative" faculty (threptikón), concerned with the ma

        For Aristotle, the soul is one, but endowed with five groups of faculties (dunámeis): (1) the "vegetative" faculty (threptikón), concerned with the maintenance and development of organic life; (2) the appetite (oretikón), or the tendency to any good; (3) the faculty of sense perception (aisthetikón); (4) the "locomotive" faculty (kinetikón), which presides over the various bodily movements; and (5) reason (dianoetikón). The Scholastics generally follow Aristotle's classification. For them body and soul are united in one complete substance. The soul is the forma substantialis, the vital principle, the source of all activities. Hence their science of the soul deals with functions which nowadays belong to the provinces of biology and physiology. [...] The nature of the mind and its relations to the organism are questions that belong to philosophy or metaphysics.

        — Ethics

        Aquinas affirms Aristotle

        Aquinas affirms Aristotle's definition of happiness as "an operation according to perfect virtue",[68][69] and that "happiness is called man's supreme good, because it is the attainment or enjoyment of the supreme good."[70] Aquinas defines virtue as a good habit, which is a good quality of a person demonstrated by his actions and reactions over a substantial period of time.[71] He writes:

        As we have said above (Article 1), virtue implies a perfection of power: wherefore the virtue of a thing is fixed by the limit of its power (De Coelo i). Now the limit of a

        As we have said above (Article 1), virtue implies a perfection of power: wherefore the virtue of a thing is fixed by the limit of its power (De Coelo i). Now the limit of any power must needs be good: for all evil implies defect; wherefore Dionysius says (Div. Hom. ii) that every evil is a weakness. And for this reason the virtue of a thing must be regarded in reference to good. Therefore human virtue which is an operative habit, is a good habit, productive of good works.

        — cardinal virtues to be prudence, temperance, justice, and fortitude. The cardinal virtues are natural and revealed in nature, and they are binding on everyone. There are, however, three theological virtues: faith, hope, and charity (which is used interchangeably with love in the sense of agape). These are supernatural and are distinct from other virtues in their object, namely, God.[72]

        In accordance with Roman Catholic theology, Aquinas argues that humans can neither wish nor do Roman Catholic theology, Aquinas argues that humans can neither wish nor do good without divine grace.[73] However, "doing good" here refers to doing good per se: man can do, moved by God even then but "only" in the sense in which even his nature depends on God's moving, things that happen to be good in some respect, and are not sinful, though if he has not grace, it will be without merit, and he will not succeed in it all the time. Therefore, happiness is attained through the perseverance of virtue given by the Grace of God,[74] which is not fully attained on earth;[75] only at the beatific vision.[76][77] Notably, man cannot attain true happiness without God.[55][78]

        Regarding emotion (used synonymously with the word "passion" in this context), which, following John Damascene,[79] Aquinas defines as "a movement of the sensitive appetite when we imagine good or evil," Thomism repudiates both the Epicurean view that happiness consists in pleasure (sensual experiences that invoke positive emotion),[80][81] and the Stoic view that emotions are vices by nature.[82] Aquinas takes a moderate view of emotion, quoting Augustine: "They are evil if our love is evil; good if our love is good."[83] While most emotions are morally neutral, some are inherently virtuous (e.g. pity)[84] and some are inherently vicious (e.g. envy).[85]

        Thomist ethics hold that it is necessary to observe both circumstances[86] and intention[87] to determine an action's moral value, and therefore Aquinas cannot be said to be strictly either a deontologicalist or a consequentialist. Rather, he would say that an action is morally good if it fulfills God's antecedent will.[88]

        Of note is the principle of double effect, formulated in the Summa, II-II, Q.64, art.7, which is a justification of homicide in self-defense. Previously experiencing difficulties in the world of Christian philosophy, the doctrine of Just War was expounded by Aquinas with this principle. He says:

        In order for a war to be just, three things are necessary. First, the authority of the sovereign by whose command the war is to be waged... Secondly, a just cause is required, namely that those who are attacked, should be attacked because they deserve it on account of some fault... Thirdly, it is necessary that the belligerents should have a rightful intention, so that they intend the advancement of good, or the avoidance of evil...

        — [89]

        1. Eternal law, which is "the type of Divine Wisdom, as directing all actions and movements;"[90]
        2. Natural law, "whereby each one knows, and is conscious of, what is good and what is evil," which is the rational being's participation in the eternal law;[91]
        3. Human or temporal law, laws made by humans by necessity;[92] andThe development of natural law is one of the most influential parts of Thomist philosophy.[94] Aquinas says that "[the law of nature] is nothing other than the light of the intellect planted in us by God, by which we know what should be done and what should be avoided. God gave this light and this law in creation... For no one is ignorant that what he would not like to be done to himself he should not do to others, and similar norms."[95] This reflects Paul the Apostle's argument in Romans 2:15, that the "work of the law [is] written in [the Gentiles'] hearts, their conscience bearing witness to them."

          Aquinas argues that the Mosaic covenant was divine, though rightfully only given to the Jews before Christ;[96] whereas the New Covenant replaces the Old Covenant[97] and is meant for all humans.[98]

          Free will

          The Thomist revival that began in the mid-19th century, sometimes called "neo-scholasticism" or "neo-Thomism," can be traced to figures such as Angelicum professor Tommaso Maria Zigliara, Jesuits Josef Kleutgen, and Giovanni Maria Cornoldi, and secular priest Gaetano Sanseverino. This movement received impetus from Pope Leo XIII's encyclical Aeterni Patris of 1879. Generally the revival accepts the interpretative tradition of Aquinas' great commentators such as Capréolus, Cajetan, and John of St. Thomas. Its focus, however, is less exegetical and more concerned with carrying out the program of deploying a rigorously worked out system of Thomistic metaphysics in a wholesale critique of modern philosophy. Other seminal figures in the early part of the century include Martin Grabmann (1875-1949) and Amato Masnovo (1880-1955). The movement's core philosophical commitments are summarized in "Twenty-Four Thomistic Theses" approved by Pope Pius X.[132]

          In the first half of the twentieth century Angelicum professors Edouard Hugon, Réginald Garrigou-Lagrange among others, carried on Leo's call for a Thomist revival. Their approach is reflected in many of the manualsAngelicum professors Edouard Hugon, Réginald Garrigou-Lagrange among others, carried on Leo's call for a Thomist revival. Their approach is reflected in many of the manuals[133] and textbooks widely in use in Roman Catholic colleges and seminaries before Vatican II.

          While the Second Vatican Council took place from 1962-1965 Cornelio Fabro was already able to write in 1949 that the century of revival with its urgency to provide a synthetic systematization and defense of Aquinas' thought was coming to an end. Fabro looked forward to a more constructive period in which the original context of Aquinas' thought would be explored.[134]

          A summary of some recent and current schools and interpretations of Thomism can be found, among other places, in La Metafisica di san Tommaso d'Aquino e i suoi interpreti (2002), by Battista Mondin, Being and Some 20th Century Thomists (2003), by John F. X. Knasas as well as in the writing of Edward Feser.[135]

          Neo-Scholastic Thomism