Metaphysics, Ontology, Philosophy

Of Simple Apprehension and Concept

by Dave Seng

Now it is impossible for a thing’s being to be caused by its essential principles, for nothing can be the sufficient cause of its own being, if its being is caused—Thomas Aquinas

In previous posts, we spent some time thinking about how the intellect works and receives reality. The intellect is potency to knowledge and can only receive that which is in act (being) through sense experience. As St. Thomas reminds us, “intelligence is compared to sense, as act is to potency”.1 It is important in this discussion to understand the distinction of simple apprehension and concept because the blurring and conflating of these categories is one of the greatest errors among Idealists. We have seen that through induction and abstraction, the essence of the external object is married to the intellect. This union of essence, or universal, with the intellect is also known as, concept, idea, species or intention. For now, we will use the term concept.

There are many different kinds of concepts, of course, and it is the task of metaphysicians and logicians to catalog, classify, and put them in proper order. For classical realists, knowledge is always of being – of that which is in some order. In this way, epistemology would be better understood as the ontology of knowing—an examination of the first principles and the order of knowing reality.

In the order of knowing, the concept is not the being of the external object, it is the essence. (Being, or that which is in act, is always matter and form.) The concept resides in the intellect as the essence or universal abstracted from external reality through the senses. To confuse the concept, or idea, with being itself is the error of the idealist.

The realist philosopher Daniel Sullivan puts it this way:

It is important to recognize that while the concept is necessary to rational knowing, it is only a means by which we know, and not that which we know. It is a necessary means, just as eyeglasses may be necessary for me to see with; yet just as it is really the table I see and not the lenses of my eyeglasses, so too it is really the thing itself I know and not my concept of it. To say that the objects of my knowing are concepts rather than things would be to fall into the trap of those philosophers called Idealists. For if all we ever know is always idea, then we can never know whether or not there is anything existing outside our mind corresponding to our ideas. Thus, following the Idealist, all reality would consist of minds and the thoughts they think.2

If one does not properly make the distinction between concept and real actual being, skepticism, uncertainty, and doubt about reality results. The perennial questions of reality will always be reduced to subjectivism. One would have no certain contact with reality outside their mind.

Drawing from St. Thomas, Dr. Adler explains:

This distinction between the id quod (that which) and the id quo (that by which) of our intellectual acts prevents us from ever saying that our concepts are that which we are conscious or aware of when we understand ideas. We could not be aware of the concepts in our minds and also at the same time be aware of their intelligible objects. If we were, we could not distinguish between them, which would mean we could not affirm that such objects exist and are shared by other minds.3

Our concepts do not tell us that things are, they tell us what things are; they reveal nature or essence, not existence. “The existence of things is outside the order of concepts,” wrote St. Thomas.4 The point to remember is that the being of an idea or concept in the mind is a different mode of existence than that of the actual external object – each belongs to a different order. Physical reality and knowing are different orders. Cognitively, humans have the ability to distinguish between that which and that by which they are aware of something. This allows one to affirm or deny the reality of something through the intellectual faculty of judgment. When the mind engages in careful and critical reflection, the essence in the intellect always points back to concrete reality. (I explained a little how the faculty of judgment works in my posts on Berkeleyan Idealism. I hope to develop the idea further as we move along.)

The process by which the intellect grasps the essence or universal is what classical realists call simple apprehension: apprehension, because the mind receives and comes to understand the essential nature of the sense object; simple, because the mind naturally takes in the intentional concept without affirming or denying it through the faculty of judgment. The operation of simple apprehension is the first act of knowing.

Without these concepts firmly understood, it is easy to fall into the error of Idealism. However, the idealist must conclude that the essence, or concept, is the cause of reality (indeed, that is the very definition of Idealism) but this is impossible because no contingent being can be the cause of its own existence.

Works Cited

Adler, Mortimer. Adler’s Philosophical Dictionary: 125 Key Terms for the Philosopher’s Lexicon. New York: Scribner, 1995.

Aquinas, Thomas. The Summa Theologica Volume 1. The Great Books of the Western World, edited by Mortimer J. Adler et al., Vol. 17, Encyclopedia Britannica, 1996.

Sullivan, Daniel. An Introduction to Philosophy: Perennial Principles of the Classical Realist Tradition. Charlotte, North Carolina: TAN Books, 2009.

Wilhelmsen, Frederick D. Man’s Knowledge of Reality: An Introduction to Thomistic Epistemology. Englewood Cliffs, N.J.: Prentice-Hall, 1956.

Notes

1Thomas Aquinas, Summa Theologica, Trans. by Father Laurence Shapcote of the Fathers of the English Dominican Province (Chicago: Encyclopedia Britannica, 1996) 1a, q.3, art. 5.

2Daniel Sullivan, An Introduction to Philosophy: Perennial Principles of the Classical Realist Tradition (Charlotte, North Carolina: TAN Books, 2009), 79.

3 Mortimer J. Adler, Adler’s Philosophical Dictionary (New York: Scribner, 1995), S. V. Idea.

4Frederick D. Wilhemsen, Man’s Knowledge of Reality: An Introduction to Thomistic Epistemology (Englewood Cliffs, N.J.: Prentice-Hall, 1956) 29.

Metaphysics, Ontology, Philosophy

On Metaphysical Realism, Where We Have Been, Where we Are Going

by Dave Seng

Being is the actuality of every form or nature; for goodness or humanity are spoken of as actual only because they are spoken of as being. Therefore being must be compared to essence, if the latter is distinct from the former, as act to potency. — St. Thomas, Summa Theologica, I, q. 3, art. 4.

Before I go any farther, I would like to recall what we have learned in the last four posts, and explain some important concepts before we get to the distinction of apprehension and concept. A solid understanding of being will allow one to fully grasp the error of idealism.

First, we have learned the following:

1. Human beings grasp reality as it is. When the senses and the mind work together symbiotically, one correctly apprehends being.

2. Being is the first principle of reality, logic, and the order of understanding. The laws of logic are properties of being.

3. Our senses are the only connection we have to external reality, therefore our senses are the first principle of understanding.

All of the above implies that the evidence of being is lost, erased, or forgotten when philosophers wrongly separate the mind from the body. (We will get to how this develops from Descartes and various idealists, later.) One does not perceive reality by the mind alone or by the senses alone, but both working together. In the human person, form and matter can not be separated.

Definitions are always important. When I write about philosophical idealism this is what I mean:

In metaphysics, idealism is the theory that all reality consists of mind and its ideas. Idealism denies the material primacy of reality. Thus, idealism is also suspicious of knowledge built exclusively on the observation of matter. There are various kinds of idealists (which, again, we will get to later). However, most idealists fall into two schools – subjective and objective idealism. Subjective idealists such as George Berkeley (1685 – 1753) hold that ideas alone exist (although he used the term ‘idea’ in novel ways) and since all ideas only exist in the mind, all reality is mind dependent. Objective idealists such as Immanuel Kant (1724 – 1804) do not deny the existence of reality, but hold that one can not know it. All idealists hold that the mind is ultimate in determining reality and are suspicious of the notion that reality (being) is the determinant of order in the world.

Because being is the touchstone of all reality, I define being as the following:

The term ‘being’ most simply refers to the fact that something exists. It can be further analyzed into abstract being (e.g., ideas, mathematical entities, etc. that exist mentally, this is sometimes called subjective existence) and concrete being (e.g., people and things that can be experienced with the senses, sometimes called real existence). Aristotle taught that the study of being as being is the primary concern for the metaphysician. In the realist tradition, the fact of being and theories about it are two distinctly separate ontological and epistemological questions.

Although we will probably not get into the grammar of being for a while, I think this quote from St. Thomas is helpful as we review where we have been (I hope it will provide a little more understanding to the previous posts). That which is in act participates in being. “Being” is taken from the verb ‘to be.’ In the grammatical expression of being, realists understand it to be both a participle and verb. Aquinas explains how being is a verb:

The verb is consignifies composition, because it does not signify this principally but secondarily. Is signifies primarily that which the intellect apprehends as being absolutely actual, for in the absolute sense is means to be in act, and thus its mode of signification is that of a verb. But, since the actuality which is principally signifies is universally the actuality of every form, whether substantial or accidental, when we wish to signify that any form or any act whatever actually exists in a subject, we express that fact by this verb is. (St. Thomas, Commentary on Aristotle’s “On Interpretation,” Book I, lect. 5, end).

Keep these ideas in mind as we discover how apprehension and concept work in the intellect. My hope here is to clarify concepts as they develop and to provide further explication.

Epistemology, Great Books, Metaphysics, Ontology, Philosophy

On the Intellect, Induction, and Abstraction

by Dave Seng

It was a good idea to call the soul ‘the place of forms’, though (1) this description holds only of the intellective soul, and (2) even this is the forms only potentially, not actually. – Aristotle

[Note: In my previous posts, I spoke about Aristotelians and Thomists as being innatist in their epistemology. I should have been more clear about this terminology because realists are not innatists in the Platonic sense. Human beings are not cognitively pre-loaded with the Platonic forms. Aristotelians are innatist in a very strict sense. What is innate, according to classical realists, is the capacity or potential to receive the form, universal, or essence of the sense object as it is in act. (See, for example, the last chapter of Aristotle’s Posterior Analytics for further explication.) I will try to develop this theme as we move along.]

In our most recent posts on Berkeleyan idealism, we learned that the mind is structured to receive and apprehend reality as it is. In other words, being is the touchstone of all reality. Being is, and can not be denied (it can not be otherwise because it would be non-being or nothing). We also learned that the intellectual faculty of judgment has both metaphysical (ontological) and epistemic or psychological aspects. When the mind is working correctly, one knows reality. Concrete reality is the proper starting point for metaphysics, not one’s theory about it (one’s theory of reality could be wrong, which is why, again, being is the touchstone of reality). In this post, I will try to explicate the basics of how the intellect works at the foundational level—at the reception of being—what Aristotelian philosophers call the intellect. This will lay the groundwork for why metaphysical realists claim that one can know reality as it is and provides further insight into the distinction between apprehension and concept—the central confusion and philosophical error among idealists, although I will develop that in upcoming posts. For now, it is important to understand how the intellect itself works.

First, what is the intellect? The word comes from the Latin terms, intus, and legere—to read within. The intellect is the cognitive capacity that humans have to think rationally, carefully, and logically about the perennial questions of existence as they find it. It is the intellect and the ability to reason which separates humans from animals. Although humans are animals, they are not simply or just animals. It should be obvious that humans have different cognitive abilities than that of animals. In addition to sense knowing, which all animals have, humans have the ability to reflect on and arrive at deeper understandings of their sense knowledge. As noted in previous posts, to sense something and to understand something is not the same thing. I can hear a foreign language but not understand it. My cat can see the same image of a sign on its retina as I do, but have no understanding of what it means, while I can easily grasp its message. Just as humans are different in kind from animals, there must be some faculty in the human mind that is different in kind from simple sense perception. This faculty is called the intellect or what philosophers in the Aristotelian and Thomist traditions call the agent intellect.

The agent intellect is a special faculty of the mind and has two important functions. First, the intellect is in potency to knowledge—it does not know to start with (it requires the act of existence to motivate it because it depends on being, as act is prior to potency). Second, as immaterial, the intellect receives the essence, universal, or form of the external object through sense perception. Aquinas reminds us, “Now it is natural to man to attain to intellectual truths through sensible things, because all our knowledge originates from sense.”1 The senses are the only connection one has to reality. Even so, what comes into the intellect has an immaterial rather than material mode of existence. The tree I am looking at through the window does not exist as a physical tree in my mind. The intellect grasps the form or essence of the sense object. This is because there is an immaterial aspect to all reality. To account for this essential reception, however, there must be a prior ability, capacity, or function in the intellect which apprehends the form of the material object. The same form of the material object exists in the intellect that exists in reality, only the mode of existence is different. This second function of the intellect is an immaterial apprehension of the material form or essence. This is what Aristotle calls the agent intellect and the reason why he calls the intellect, or soul, “the place of the forms.”2 The agent intellect apprehends the essence of the thing perceived. The nature of the agent intellect is to receive the object of sense perception3.

A question remains, however. How do the forms or universals get into the intellect?

The intellect is in potency to knowledge and has a capacity to receive the essence of an external object. Now, it is important to understand how the form or essence of a thing is delivered to the intellect. Briefly, this is accomplished by induction and abstraction. Induction, or inductive reasoning, is the logical process of thinking in which the conclusion follows from experience, examination of particulars, and arriving at generalized or universal principles—for Aristotelians, the foundation of all subsequent reasoning. Aristotle held that wider and wider generalization is derived from repeated empirical experiences of particular things until the essence or universal concept is established in the intellect. Philosopher Ed Miller puts Aristotelian inductive reasoning it this way:

From the experience of the particular man Callias, the man Socrates, the man James, the man Tad, the man Bill … the intellect derives the general or universal idea of man, that is man as such. From the experience of the particular dog Fido, the dog Lassie, the dog Rover, the dog Flip … the intellect derives the universal idea dog. And the universal ideas—man, dog, and innumerable other concepts derived from experience in the same manner—become the tools and building blocks of all reasoning. They then make it possible to say and know, “Socrates is a man,” “In fourteen hundred and ninety-two Columbus sailed the ocean blue,” etc.4

Aristotle compares the formation of the universal in the intellect to the formation of soldiers making a stand against a wartime enemy:

We conclude that these states of knowledge are neither innate in a determinate form, nor developed from other higher states of knowledge, but from sense-perception. It is like a rout in battle stopped by first one man making a stand and then another, until the original formation has been restored. The soul is so constituted as to be capable of this process. . . . When one of a number of logically indiscriminable particulars has made a stand, the earliest universal is present in the soul: for though the act of sense-perception is of the particular, its content is universal—is man, for example, not the man Callias. A fresh stand is made among these rudimentary universals, and the process does not cease until the indivisible concepts, the true universals, are established: e.g. such and such a species of animals is a step towards the genus animal, which by the process is a step towards a further generalization. Thus it is clear that we must get to know the primary premisses by induction; for the method by which even sense-perception implants the universal is inductive.5

In fact, Aristotle believes induction to be the basis of all other knowledge:

From experience again—i.e. from the universal now stabilized in the soul, the one beside the many which is a single identity within them all—originate the skill of the craftsman and the knowledge of the man of science, skill in the sphere of coming to be and science in sphere of being.6

Metaphysics, the study of being as being, is the science in the sphere of being. In other words, metaphysics is a kind of science in the Aristotelian and Thomist tradition. Being is at the center of whatever is thought or done. One can not change the oil in his truck or complete a math equation without referencing being. Being, however, is the first act of knowing. The intellect can only understand the universal or essence of any external object through induction.

Aristotle’s notion of induction is very similar to the concept of abstraction put forward by St. Thomas. Aquinas focuses on the idea that the mind can remove, withdraw, or pull out the concept of redness from viewing various red objects. One understands the concept of justice by examining just actions. Abstraction is a general idea, universal, or essence that the intellect removes from the multiple expressions of the same form found in the particular instances of it (the essential nature of the particular whether it be dog, cat, chair, human, or concepts such as the good, true, beautiful etc.).

St. Thomas helps us understand how the intellect moves from the particular to the universal (here “intelligible species” means essence. “Phantasms” are the mental images of things):

Our intellect cannot know the singular in material things directly and primarily. The reason of this is that the principle of singularity in material things is individual matter, while our intellect … understands by abstracting the intelligible species from such matter. Now what is abstracted from individual matter is the universal. Hence our intellect knows directly the universal only. But indirectly and as it were by a kind of turning back (reflectio), it can know the singular, because … even after abstracting the intelligible species, the intellect, in order to understand actually, needs to turn to the phantasms in which it understands the species. … Therefore it understands the universal directly through the intelligible species, and indirectly the singulars represented by the phantasms. And thus it forms the proposition, “Socrates is a man.”

Classical realists, then, begin with being—the concrete particular things encountered in the sensible external world. Being is more than physical reality but never less than it. With the universal firmly in place in the intellect one is enabled to return and know reality through reflection and judgment. One can genuinely think about reality, know it, and express it, “Socrates is a human being.”

For Further Reading:

Holloway, M., “Abstraction from Matter in Human Cognition”, The Modern Schoolman, Vol. XXIII (1946), pp. 120 – 130.

For a more general introduction to Thomist epistemology see:

Wilhelmsen, Fredrick. Man’s Knowledge of Reality: An Introduction to Thomistic Epistemology. Englewood Cliffs, N.J.: Prentice-Hall, Inc., 1956.

I wrote about the Aristotelian distinctions of act and potency here.

Works Cited

Aquinas, Thomas. The Summa Theologica Volume 1. The Great Books of the Western World, edited by Mortimer J. Adler et al., Vol. 17, Encyclopedia Britannica, 1996.

Aristotle. The Works of Aristotle Volume 1. The Great Books of the Western World, edited by Mortimer J. Adler et al., Vol. 7, Encyclopedia Britannica, 1996.

Miller, Ed. Questions that Matter: An Invitation to Philosophy. New York: McGraw-Hill, 1996.

Footnotes

1Thomas Aquinas, Summa Theologica, Trans. by Father Laurence Shapcote of the Fathers of the English Dominican Province (Chicago: Encyclopedia Britannica, 1996) 1a, q.1, art. 9.

2Aristotle, On the Soul (De Anima), Trans. by J. A. Smith (Chicago: Encyclopedia Britannica, 1996) 661.

3 While we are distinguishing the important faculties of the intellect, it is also very important to be aware that the whole person is involved in knowing. This requires a bit of development and goes beyond the scope of this post but I plan on explicating this notion in time. For now, it is important to understand that for those in the Aristotelian and Thomist tradition, the entire person is involved in apprehending reality. This is because form and body (matter and form) are united and should never be separated. Not only does the individual know and understand things through deduction and induction, humans also know through connatural knowledge—the lived and embodied contact one has with others and reality itself. This involves knowing through empathy, lived human experience, intuition, and the contact of the intellect with the truth of reality itself by other holistic ways of knowing such as imaginative literature, the arts, and history. Embodied knowledge means knowledge through the whole person and by way of all the arts and sciences. The Platonic tradition sees form and matter as separate which, if unchecked, leads to idealism. Idealism is the result of disembodied knowledge, a disembodied epistemology. Platonist metaphysics rests on the separation of form from matter and provides the foundation for the error of idealism.

4Ed Miller, Questions That Matter: An Invitation to Philosophy (New York: McGraw-Hill, 1996) 235.

5Aristotle, Posterior Analytics (Analytica posteriora), Trans. by G.R.G Mure (Chicago: Encyclopedia Britannica, 1996) 136.

6Aristotle, Posterior Analytics, 136.

Intellectual History, Metaphysics, Philosophy

Berkeley, Classical Realism, and the Metaphysical First Principles of Being, Part Two

by Dave Seng
St. Thomas Aquinas, also called Doctor Angelicus (Latin: “Angelic Doctor”),  born 1224/25,—died March 7, 1274.

Part one can be found here. This is part two of a three part series which reflects on Berkeleyan idealism in light of classical realism.

A foundational concept in Berkeley’s philosophy is that reality depends on a perceiver in order for it to be (the esse in his famous dictum). And this is the point of contention for classical realists. Is it correct to say that reality is structured in such a way that it must be perceived to exist? (Additionally, an outright denial of the existence of matter seems problematic and is, in fact, Gnostic.) Classical realism takes both perception and objective reality seriously because sense experience is the only connection one has to the world. The realist finds the entire project of proving an external world to be supremely uninteresting and quite unnecessary. Regarding the faculties of the mind, the act of perception is different from other cognitive abilities like thought, memory, or imagination. Thinking is not the same as having a sense perception. One can think through an issue or problem, recall a memory, or use one’s imagination (such as reading a work of fiction or pondering the existence of centaurs). When these faculties, or acts of the mind, are engaged one can always ask the additional reflective question of whether or not they exist in external reality. When it comes to the faculty of perception, however, one cannot separate one’s perception of an object from its actual existence in reality. Normal perception is always the perception of an external object. If that were not the case, there would be no difference between reality and hallucination. When one asks about hallucinations, external objective reality is assumed in the question, or it would not be a question.1 Perception is what gives human beings the ability to distinguish between appearance and reality (in order to correct a faulty sense appearance, one simply has another sense experience). The faculty of imagination, however, consists of the ability to think of objects that do not exist in reality. In contrast, the faculty of perception is always of something, an external object. Classical realists hold that humans are cognitively structured to be of, about, and oriented towards reality. It makes little sense to say one has a physical perception of a tree and, at the same time, that the tree does not exist. The logical laws of non-contradiction, identity, and excluded middle still hold with sense perception. It does no good to deny external reality. When the mind works correctly, there is no need to prove an external world. Human perception is always of something. In metaphysical terms, that which is cannot be denied.

Berkeley’s conflation of thinking with perception utterly confuses the most important aspects of reality itself—the subjective and objective, appearance and reality, being and becoming, the one with the many, and ultimately equates thought, or mind, with Being. Instead of clarifying reality or explicating the nature of reality, Berkeley only adds more confusion to these ultimate questions. If Berkeley’s interpretive scheme of reality is correct, there is no way to explore the metaphysical nature of reality. The field of metaphysics, itself, would be impossible. The rejection of any reality external to one’s mind undermines the task of metaphysics which is to discover the objective first principles of being as being, at least according to the Aristotelian definition of metaphysics.

Further, classical realists hold to compresence—the idea that minds and objects are both part of reality and co-related. Because human beings live in a common world of sense, they can also share a common world of thought and intellectual engagement. As Alfred North Whitehead explains, “I do not understand how a common world of thought can be established in the absence of a common world of sense” (178). Human beings share the same basic reality and the mind is tuned to the concrete requirements of objective existence. Reality has its own intractable way of being and it is objectively intelligible, discoverable, and shareable with others through the tools of reason—sometimes by way of induction, other times by deduction, and sometimes both working together. Being itself is the unifying standard of all thought and physical activity. The realist, therefore, maintains that all thought and human action takes place in objective time and space.

As extreme as Berkeley appears to be, it is important to take a closer examination of his perspective, and we will explore this further in upcoming posts. For now, keep in mind that no great philosopher or author is completely wrong. Berkeley’s idealism forces one to think about the nature of reality at a deeper level. Perhaps one reason for including Berkeley as one of the great Western philosophers that (although epistemically wrong), he forces one to think more carefully, rationally, and critically about the most fundamental questions of reality. Even when a thinker is wrong, an examination of the position is still instructive. Berkeley raises several questions that the realist wisely takes seriously. How should one think about reality or being? What role does the mind have in knowing reality? And what are the ultimate principles of reality, if any?

While idealists such as Berkeley insist that reality is determined by the mind, or immaterial spirit, realists like Aristotle and Aquinas pose a different strategy for understanding reality and offer a way to think about being that neither denies the role of the mind, nor rejects external reality. When it comes to epistemology, realists believe that there must be first principles of knowledge. An examination of these first principles will demonstrate the role that the intellect plays in knowing reality. The first principles of knowledge are self-evident and foundational to all other knowledge.

All the sciences are derived from basic self-evident first principles. Aquinas puts it this way, “The principles of any science are either in themselves self-evident, or reducible to the knowledge of a higher science” (Ia, q. 1, a. 2 ). And, “The word ‘principle’ signifies only that from which another proceeds: For anything from which something proceeds in any way we call a principle” (Ia, q. 33, a. 1). Self-evident truths are principles that are foundational to all knowledge, and are impossible to deny (such as logical truth, the law of noncontradiction, mathematical truth such as the axioms of geometry, and moral truths such as the proposition that it is always wrong to rape women)2. Self-evident truths are the starting points for any scientific or philosophical inquiry. First principles do not provide the content of reality, rather, they are what make knowledge of reality possible. Classical realists do not deny that the mind has a role when it comes to understanding reality.

Aquinas also refers to first principles that are reducible to the knowledge of a higher science. This occurs when, for example, one understands that music relies on mathematical formulas, or the scientific method rests on the ultimate metaphysical principles of the law of causality, law of predictive uniformity, law of noncontradiction, and others. In fact, it was Aristotle who claimed that it was the mark of an uneducated person not to realize that there must be certain first principles of reality such as the foundational law of noncontradiction (Aristotle, Vol. 7, 525).

In our next post, we will discuss the first principles of being, which are properties of reality and through which we come to understand what is. The first principles of reality are both ontological and epistemic in nature.

1Hallucination is pathological. When the mind is functioning correctly, perception is not pathological, it is normative. When determining between reality and hallucination, external objective existence is assumed.

2Self-evident truths, or first principles, are often intuitive but they can become explicit, usually through education. They are impossible to deny because they must be assumed in any attempt to deny them.

Works Cited

Aquinas, Thomas. The Summa Theologica: 1. Great Books of the Western World. Vol. 17. Encyclopedia Britannica, Inc., 1999.

Aristotle. The Works of Aristotle: 1. Great Books of the Western World. Vol. 7. Encyclopedia Britannica, Inc., 1999.

Berkeley, George. The Principles of Human Knowledge. Great Books of the Western World. Vol. 55. Encyclopedia Britannica, Inc., 1999.

Whitehead, Alfred North. Science and the Modern World. Great Books of the Western World. Vol. 55. Encyclopedia Britannica, Inc., 1999.