Thomas was a theologian and a Scholastic philosopher.[51] However, he never considered himself a philosopher, and criticized philosophers, whom he saw as pagans, for always "falling short of the true and proper wisdom to be found in Christian revelation".[52] With this in mind, Thomas did have respect for Aristotle, so much so that in the Summa, he often cites Aristotle simply as "the Philosopher." Much of his work bears upon philosophical topics, and in this sense may be characterized as philosophical. Thomas's philosophical thought has exerted enormous influence on subsequent Christian theology, especially that of the Roman Catholic Church, extending to Western philosophy in general. Thomas stands as a vehicle and modifier of Aristotelianism and Neoplatonism.
Commentaries on Aristotle
Thomas wrote several important commentaries on Aristotle, including On the Soul, Nicomachean Ethics and Metaphysics. His work is associated with William of Moerbeke's translations of Aristotle from Greek into Latin.
Epistemology
Thomas believed "that for the knowledge of any truth whatsoever man needs divine help, that the intellect may be moved by God to its act."[53] However, he believed that human beings have the natural capacity to know many things without special divine revelation, even though such revelation occurs from time to time, "especially in regard to such (truths) as pertain to faith."[54]
Revelation
Thomas believed that truth is known through reason (natural revelation) and faith (supernatural revelation). Supernatural revelation has its origin in the inspiration of the Holy Spirit and is made available through the teaching of the prophets, summed up in Holy Scripture, and transmitted by the Magisterium, the sum of which is called "Tradition". Natural revelation is the truth available to all people through their human nature; certain truths all men can attain from correct human reasoning. For example, he felt this applied to rational ways to know the existence of God.
Though one may deduce the existence of God and his Attributes (One, Truth, Good, Power, Knowledge) through reason, certain specifics may be known only through special revelation (such as the Trinity). In Thomas's view, special revelation is equivalent to the revelation of God in Jesus Christ. The major theological components of Christianity, such as the Trinity and the Incarnation, are revealed in the teachings of the Church and the Scriptures and may not otherwise be deduced.
Supernatural revelation (faith) and natural revelation (reason) are complementary rather than contradictory in nature, for they pertain to the same unity: truth.
Creation
As a Catholic, Thomas believed that God is the "maker of heaven and earth, of all that is visible and invisible." Like Aristotle, Thomas posited that life could form from non-living material or plant life, a theory of ongoing abiogenesis known as spontaneous generation:
Since the generation of one thing is the corruption of another, it was not incompatible with the first formation of things, that from the corruption of the less perfect the more perfect should be generated. Hence animals generated from the corruption of inanimate things, or of plants, may have been generated then.[55]
Additionally, Thomas considered Empedocles' theory that various mutated species emerged at the dawn of Creation. Thomas reasoned that these species were generated through mutations in animal sperm, and argued that they were not unintended by nature; rather, such species were simply not intended for perpetual existence. This discussion is found in his commentary on Aristotle's Physics:
The same thing is true of those substances which Empedocles said were produced at the beginning of the world, such as the ‘ox-progeny’, i.e., half ox and half man. For if such things were not able to arrive at some end and final state of nature so that they would be preserved in existence, this was not because nature did not intend this [a final state], but because they were not capable of being preserved. For they were not generated according to nature, but by the corruption of some natural principle, as it now also happens that some monstrous offspring are generated because of the corruption of seed.[56]
[edit] EthicsThomas's ethics are based on the concept of "first principles of action."[57] In his Summa Theologica, he wrote:
Virtue denotes a certain perfection of a power. Now a thing's perfection is considered chiefly in regard to its end. But the end of power is act. Wherefore power is said to be perfect, according as it is determinate to its act.[58]
Thomas defined the four cardinal virtues as 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. These are supernatural and are distinct from other virtues in their object, namely, God:
Now the object of the theological virtues is God Himself , Who is the last end of all, as surpassing the knowledge of our reason. On the other hand, the object of the intellectual and moral virtues is something comprehensible to human reason. Wherefore the theological virtues are specifically distinct from the moral and intellectual virtues.[59]
Furthermore, Thomas distinguished four kinds of law: eternal, natural, human, and divine. Divine law is the decree of God that governs all creation. Natural law is the human "participation" in the eternal law and is discovered by reason.[60] Natural law, of course, is based on "first principles":
. . . this is the first precept of the law, that good is to be done and promoted, and evil is to be avoided. All other precepts of the natural law are based on this . . .[61]
The desires to live and to procreate are counted by Thomas among those basic (natural) human values on which all human values are based. According to Thomas, all human tendencies are geared towards real human goods. In this case, the human good in question is marriage, the total gift of oneself to another that ensures a family for children and a future for mankind.[62]
Human law is positive law: the natural law applied by governments to societies. Divine law is the specially revealed law in the scriptures.
Thomas also greatly influenced Catholic understandings of mortal and venial sins.
Thomas denied that human beings have any duty of charity to animals because they are not persons. Otherwise, it would be unlawful to use them for food. But this does not give us license to be cruel to them, for "cruel habits might carry over into our treatment of human beings."[63]
Thomas contributed to economic thought as an aspect of ethics and justice. He dealt with the concept of a just price, normally its market price or a regulated price sufficient to cover seller costs of production. He argued it was immoral for sellers to raise their prices simply because buyers were in pressing need for a product.[64][65]
Intentionality
The pioneer of neurodynamics, cognitive neuroscientist Walter Freeman, considers the work of Thomas important in remodeling intentionality, the directedness of the mind toward what it is aware of.
Psychology
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Aquinas maintains that a human is a single material substance. He understands the soul as the form of the body, which makes a human being the composite of the two. Thus, only living, form-matter composites can truly be called human; dead bodies are “human” only analogously. One actually existing substance comes from body and soul. A human is a single material substance, but still should be understood as having an immaterial soul, which continues after bodily death.
Ultimately, humans are animals; the animal genus is body; body is material substance. When embodied, a human person is an “individual substance in the category rational animal.”[66] The body belongs to the essence of a human being. In his Summa Theologica, Aquinas clearly states his position on the nature of the soul; defining it as “the first principle of life.”[67] The soul is not corporeal, or a body; it is the act of a body. Because the intellect is incorporeal, it does not use the bodily organs, as “the operation of anything follows the mode of its being.”[68]
The human soul is perfected in the body, but does not depend on the body, because part of its nature is spiritual. In this way, the soul differs from other forms, which are only found in matter, and thus depend on matter. The soul, as form of the body, does not depend on matter in this way.
The soul is not matter, not even incorporeal or spiritual matter. If it were, it would not be able to understand universals, which are immaterial. A receiver receives things according to the receiver’s own nature, so in order for soul (receiver) to understand (receive) universals, it must have the same nature as universals. Yet, any substance that understands universals may not be a matter-form composite. So, humans have rational souls which are abstract forms independent of the body. But a human being is one existing, single material substance which comes from body and soul: that is what Thomas means when he writes that “something one in nature can be formed from an intellectual substance and a body,” and “a thing one in nature does not result from two permanent entities unless one has the character of substantial form and the other of matter.”[69]
The soul is a "substantial form"; it is a part of a substance, but it is not a substance by itself. Nevertheless, the soul exists separately from the body, and continues, after death, in many of the capacities we think of as human. Substantial form is what makes a thing a member of the species to which it belongs, and substantial form is also the structure or configuration that provides the object with the abilities that make the object what it is. For humans, those abilities are those of the rational animal.
These distinctions can be better understood in the light of Aquinas’ understanding of matter and form, a hylomorphic ("matter/form") theory derived from Aristotle. In any given substance, matter and form are necessarily united, and each is a necessary aspect of that substance. However, they are conceptually separable. Matter represents what is changeable about the substance - what is potentially something else. For example, bronze matter is potentially a statue, or also potentially a cymbal. Matter must be understood as the matter of something. In contrast, form is what determines some particular chunk of matter to be a specific substance and no other. When Aquinas says that the human body is only partly composed of matter, he means the material body is only potentially a human being. The soul is what actualizes that potential into an existing human being. Consequently, the fact that a human body is live human tissue entails that a human soul is wholly present in each part of the human.
