Beginning Metaphysics II: Defining Existence

Metaphysics is the science that studies being as being. But in order to study being, we must know what “being” is in the first place. This is much easier said then done, because in a very real sense, being is almost not something definable, not something susceptible of definition. Being or existence is something taken for granted, quite literally. It is the most abstract, and hence the most vague, of all possible concepts. It is likewise the most fundamental of all concepts. It is something we quite obviously can recognize, but not something we can very easily understand.

In technical logic, a definition consists of a genus and specific difference. To define something is first to classify it, to say what type of thing it is, and then to specify it, differentiate it from the other things within that same class/type, mark it as unique in some way. A simple and well known example is Aristotle’s definition of humanity as “rational animals”. The “kind” of thing humans are is animals; what separates us from other animals is our distinctive quality of thought/reason/consciousness. Or we might define a triangle as a “shape with three sides and three angles”.

But from this, it should be immediately clear why defining “existence” is so difficult. For all categories and classes of things just assume the existence of the thing being defined. “Existence” as such is common to every category, every genus, every species. Furthermore, definition involves separating something from everything else, but one cannot “separate” existence in such a manner. We could separate existence from “nothing” or “non-existence”, but non-existence by definition does not exist, so it is not something real from which we can separate existence; it is merely conceptual. Even if we can separate them, in what common class could we place the two, even conceptually, in order to distinguish them? In other words, when we define humanity, we place into the genus of “animals”, and then state what makes this particular animal different from all the others. But by putting something into a genus, you are acknowledging something really common and similar between it and all other entities in that genus. It is to provide a base for comparison and distinction, a common ground. But what common ground could there possibly be between existence and non-existence? We might say that each is a “state” of something. But is this state actually existent, or non-existent? If it is actually existent, one could hardly place non-existence into it as a genus. If it is not existent, then it isn’t real, and one could hardly place existence into it as a genus.

So we might not be able to offer a precise definition of existence as such. But, obviously, we still recognize it, we still know what it is in a general sense. How?

The same way we know anything at all: by its action. When we say that a human being is a rational animal, we are asserting the existence of a thing and identifying a certain way in which it acts, a way in which it behaves, certain qualities/properties it exhibits, a certain way it is. For humans, this includes existing as living organisms, and existing as living organisms which think. Similarly, we also recognize existence by action. Namely, we recognize existence by its action of not not existing, by “standing out” from non-existence, as it were, and “presenting itself” to reality. W. Norris Clarke writes:

What does “is” mean? It is so fundamental that it is impossible to define it by anything clearer, or by setting it off as a class within a wider class, as is done in ordinary definitions, for outside of it there is nothing. We already know implicitly what it means, because we know how to use it meaningfully, though it is not always easy to spell it out explicitly further. Metaphysics tries to do this. One way is to call up paraphrases, for example: “exists,” or–perhaps more evocative–“presents itself”: a being is that which is actually present in some way, presents itself as standing out from the darkness of non-being into the light of being” [1].

George P. Klubertanz lists as one of the attributes of any real being that it is “acting or being acted upon” [2], and comments that “In the proper sense of the word, a real being is an actual being, one which is not merely an object of the mind or merely possible, but is actually in itself” [3]. But this brings us to a further distinction than just “being” generally.

We have said that we recognize existence, even if we cannot precisely define it, insofar as it acts, presents itself from nothingness. So if I were to set a glass of water down on a table, and ask “does this glass exist?” your response, if indeed there is a glass there, would be “yes, it does exist.” But if I were to ask “does Alexander the Great exist?” that suddenly becomes much more complicated. Or if I were to ask “does planet Jupiter exist five million years from now?” The correct answer might be “I don’t know,” but in an even more fundamental sense the answer is just “no,” since what might exist five million years from now does not exist as such here and now, is not actually present here and now. It is possible for it to exist five million years from now, but it does not as of yet actually do so.

We could also ask “do unicorns exist”, to which most people would easily enough respond “no.” But if unicorns do not in some sense exist, how is it that we’re asking a question about them? In other words, in order to meaningfully communicate a question in reference to something such as a “unicorn”, that thing must be in some way intelligible. And how can something that has no existence whatsoever at all be intelligible? At the same time, we recognize that obviously there is no actually existing entity that has the properties and characteristics of our understood idea of a unicorn. So this means we must make a distinction between what actually, really exists, what is actually present to us externally, and what exists mentally, what exists as an idea in our intellect. In Thomistic metaphysics, these distinct aspects of being are referred to as “real being” and “mental being” respectively. Real being exists completely on its own, independent from any “knowers”, whereas mental being depends entirely on some mind or thought for its existence; it exists only “in” a mind, as idea or concept.

The fact that mental being itself is entirely dependent upon some mind for its existence immediately necessitates that mental being in general is dependent upon real being in general. For if the mind which thinks is not real, not actually existent, then it could hardly think at all, and hence could not actually generate mental being at all. Whether this really existent mind is somehow identical to the brain, or distinct therefrom, is an object of philosophy of mind, and is irrelevant for our purposes now. All that matters here is recognizing that mental being depends entirely on real being. As Clarke puts it, “All mental beings are in some way derived from and refer back to the order of real being” [4].

The next important distinction to make has to do with application of terms. In Aristotle’s Categories, he begins with a discussion of “univocality” and “equivocality”. Since I hope to be writing specifically about Aristotle’s Categories in the future, I won’t quote therefrom here. Basically, a univocal term is one which is applied to different things, all of which are exactly the same in meaning. For example, the term “human” is precise and distinctive, it applies only to those beings which fit its exact definition. There could be no real, meaningful sense in which one could refer to a tree as a “human” and expect to convey intelligible communication. A univocal term has strict and defined limits.

An equivocal term is one which is applied to various different things, but with completely different meanings. In english, we often refer to these technically as “homonyms”, words which have the same spelling but different meanings. For example, “right” as in to do the right thing, and “right” as in the opposite of left. There is usually no larger significance in relationship between these words other than their accidental linguistic alignment.

Finally, the most important in Thomistic metaphysics is an analogous term, which might be seen as being in the middle between the two extremes of univocal and equivocal terms. An analogous term is one which “is applied to several different subjects according to a meaning that is partly the samepartly different in each case” [5]. Analogous terms are more flexible than univocal terms, they can “shift” their meanings relative to the thing they are being applied to, but they are still more than just an “accidental linguistic alignment”, they convey some real meaningful relationship/similarity. Clarke provides a simple example: “strength of muscles, strength of an argument, strength of will” [6]. Obviously, in each case we are referring to very different things, and hence our meaning of “strength” will differ proportionately to each. Physical strength is very different from logical strength which is very different from mental strength. And yet, we do not want to say that they are all completely, totally different in meaning, that they bear no resemblance, no meaningful relationship, for then our statements are just unintelligible. In every case, strength seems to refer to some sort of power, some sort of ability for action that has been exercised/trained/honed. There is some common base in meaning. This becomes extremely important as we move on, since almost every term we can apply to God, we can only do so in an analogous sense. To apply an analogous term to God is to say something real and true about Him, but it is not to do so definitively. As we shall see, God, for Aquinas, is in a very real sense quite mysterious.

St. Thomas and his metaphysical system differs from many other systems precisely in holding “being” to be an analogous concept. We cannot actually defend this in depth here, since to wholly grasp why we must first understand his essence/existence distinction. But we can offer a general why thinking so makes sense.

Consider, by way of example, a univocal term such as triangle. The term “triangle” is clearly restricted in application to those objects which fit within its strict limits. Anything that does not have three sides and three angles cannot rightly be called a triangle. In order to be a triangle, a thing must fit the basic “standard” which its definition offers. Of course, actual triangles that do exist can be quite different. They can be all different colors, they can be all different sizes, they can be drawn on paper or on chalk boards or on computer screens. They can be isosceles or scalene or equilateral. So the term “triangle” clearly has some space for differentiation. But all of these, in order to be a triangle, must align with the essential definition of having three sides and three angles.

But now consider “existence” or being. To say that something exists is not to say what it is, a fact that, as we shall see in the next post, becomes the very foundation for all of St. Thomas’s metaphysics. An object that exists can exist as living or inanimate, as material or (arguably) immaterial, as plant or animal or human or star or planet or atom or electron, etc., etc., etc. But, even more importantly, things that exist can exist within different “categories” as Aristotle calls them. Substance exists, but so do accidents; and the way in which they exist is profoundly different.  Different individual beings and types of beings exist, but they do not all exist in the same way, as the same thing or type of thing.So “being” cannot be univocal; it must be analogous.

Another way to think of this is in terms of logical identity. To say of any entity that it is an X is to say that it is not a non-X. A non-triangle is, by definition, not a triangle. A non-triangle can be literally any other thing that exists or possibly exists, but its definition necessarily precludes it from being a triangle. So for an entity to be both a triangle and a non-triangle at the same time and in the same respect is necessarily logically impossible. A red triangle and a blue triangle are, insofar as they are triangles, logically identical. A univocal term is one which applies to logically identical entities. But both a triangle and a non-triangle exist, and yet they are not logically identical entities (in fact, they are logically contradictory). A horse and an elephant are not logically identical, and yet we would apply “being” to both. So being must be an analogous term. It does not mean the same thing to exist as an elephant as it does to exist as a horse, and yet we want to say that there is some commonality between the two, that “existence” has a common base in meaning even when applied to drastically different types of beings. Klubertanz writes:

“Being, in any singular existent, cannot be entirely and exactly the same as it is in any other thing. It must in each instance be and be known as a definite singular thing uniquely ordered to its own act of existing. It must in each instance include all that is unique and proper to the singular individual, and so it cannot be an univocal intelligibility” [7].

Most of what has been said in this post has just been an introduction to terms and to a way of thinking about existence. In the next post in the series, we will delve into Aquinas’s “essence/existence” distinction, which is the foundation, and the crux, of his whole metaphysical system.



[1]. Clarke, W. Norris. The One and the Many: A Contemporary Thomistic Metaphysics. Notre Dame: University of Notre Dame Press, 2001. Print, 26.

[2]. Klubertanz, George P. Introduction to the Philosophy of Being. 2nd edition. Eugene: Wipf and Stock Publishers, 2005. Print, 49.

[3]. Ibid., 28.

[4]. Clarke. The One and the Many. 30.

[5]. Ibid., 45.

[6]. Ibid.

[7]. Klubertanz. Introduction to the Philosophy of Being. 66.




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