What Is Metaphysics?

What is Metaphysics According to Thomas Aquinas?

The name of metaphysics stands for a broad range of human activities and literature. Perhaps the only binding and distinguishing characteristic of this range is that of somehow relating to what, in principle, cannot be seen or felt or heard or in any way sensed. Metaphysics sometimes encompasses inquiry into angels and demons, purely rationalistic notions about God, or the exploration of occult forces of nature and of the human spirit. The great bulk of what passes for metaphysics in the popular mind bears little resemblance or relation to genuinely rigorous, scientific or philosophic reasoning. Indeed, even among some of the philosophically rigorous, anything bearing the name metaphysics receives an intellectually cool reception precisely because of the association with the non-material that is inextricably worked into its name (metaphysics derives from the Greek: ta meta ta phusika, the beyond-the-physical, or what is studied after physics).

The problem of defining the nature of metaphysics also may be seen by examining it in relation to other sciences. Given the fact that everything that one can know either is sensed or knowledge of it is derived from the senses, and so is in some way dependent on physical reality, there arises the problem of finding a subject- matter unique to metaphysics. Granted that all sciences study things, either some class of material things or some aspect of them (e.g. physics studies changing being; mathematics, quantified being; logic, beings of reason) what does metaphysics study that is not studied by physics, mathematics or logic, but is unique to itself? Or put another way, what does the metaphysician know about things that the physicist, or mathematician or logician does not?

The answer given by Aristotle, and by St. Thomas Aquinas after him, is that metaphysics studies being as being. This implies, and the diversity of the other sciences confirms, that being can be studied in some way other than as being, e.g. as changing, etc. But the fact remains that everything we directly experience through our external senses is changeable being, e.g. rocks and trees. And following Aristotle’s analysis, things are changeable insofar as they are material. As essentially changeable, such objects of sensation are popularly described as being made up out of “stuff.”

“The term (matter) pretty well corresponds in its use to some uses of the word ‘stuff’ in English. …(W)hen the stuff that Miss T. eats turns into Miss T., Aquinas would say that the same matter was first (say) bread and then part of a human body”

G.E.M. Anscombe and P. Geach, Three Philosophers, (Ithaca, New York: Cornell University Press, 1961), p. 69.

So, we may inquire how one can come to know being as distinct from stuff, if we take “stuff” to mean the matter of the things which we see and touch. And it is not immediately obvious that being means anything other than the things which are made out of some common stuff. So the question becomes: How can metaphysics study being as being in contradistinction from physics, which studies being as material and changing, if all we can directly know is changing being?

In the thought and writings of St. Thomas Aquinas, metaphysics holds an honored place among the speculative rational sciences and philosophical disciplines. It is the queen of rational disciplines and receives the name of wisdom. In the Prooemium to his Commentary on the Metaphysics of Aristotle, Aquinas explains why the science enjoys the preeminence that it does. He also endeavors to give a rationale for how the science ought to be named, since this field of inquiry, so far only referred to as metaphysics, traditionally has borne other names, i.e. First Philosophy, and Theology. Now, while this philosophical enterprise involves immateriality in all three of the aspects to which these names correspond, that aspect that is the science’s core is a treatment of immateriality in a qualified sense.

According to Aquinas, three features characterize speculative, philosophical wisdom: being most causal/certain, most universal, and most immaterial. These features correspond to the realities that are treated by the science: God, being and its principles, and subsistent immaterial realities (i.e. angels and the rational soul). Likewise, to these features there also correspond three names. The most intelligent speculative science which orders all others is called First Philosophy insofar as it explains all things in terms of the first cause of things. Insofar as the most intelligent science seeks to explain being and its principles, philosophical wisdom carries the name of Metaphysics. And finally, Theology is the name of the most intelligent science according as this speculative wisdom examines immaterial subsistents (e.g. God and angels) through their causal relation to material things.

But the question remains as to which name is most proper, and which feature most essential to this science. Now the investigations of First Philosophy and philosophical theology are conducted only by the relation they have to the subject of metaphysics. What characterizes First Philosophy and philosophical theology enters into the consideration of wisdom only because God and immaterial subsistents are related to being and its principles. The pursuer of speculative wisdom studies the First Principle and separate intellectual substances only in order to explain the most universal characteristics of all things. Thus, Aquinas concludes that speculative wisdom is essentially the study of the most universal aspect of real things, their being.

And so, Metaphysics is the proper name of this speculative philosophical wisdom, and not First Philosophy nor Theology (although only these latter two were used by Aristotle himself to characterize wisdom, and not metaphysics). Thus, positively immaterial substances, i.e. God and intellectual substance, are not the proper subject of metaphysics. Rather being as being (ens inquantum ens) or being in general or common being (ens commune) is the subject matter of metaphysics. Aquinas concludes to ens commune as the subject of metaphysics because ens commune is the genus, i.e. the intelligible formality , which metaphysics hopes to explain by appealing to positively immaterial things.

…Consequently, it must be the office of one and the same science to consider separate substances and being- in-general (ens commune) which is the genus of which the separate substances mentioned above are the common and universal causes…. For the subject of a science is the genus whose causes and properties we seek, and not the causes themselves of the particular genus studied, because the knowledge of the causes of some genus is the goal to which the investigation of the science attains.

Thomas Aquinas, Commentary on the Metaphysics of Aristotle, prooem., John P. Rowan, trans. (Chicago: Henry Regnery Co., 1961), pp. 1-2.

Immaterial realities, things having in themselves no “stuff,” become known within the science of metaphysics as the common and universal causes of being in general. They fall within the science only in order to explain ens commune. However, knowledge of the immaterial is necessary in order for ens commune to be known. That is, the nature of being as being requires knowledge of some immaterial realities outside and prior to the science of metaphysics, though this point is not explicitly asserted in the prooem. to Aquinas’ Commentary on the Metaphysics.

Aquinas thus applies the name metaphysics to the science of speculative wisdom in virtue of the subject matter of the science, being in general. Yet he claims that being in general is predicated of those things separate from matter, i.e. stuff, both in intelligible constitution (ratio) and in being (esse).

Now although the subject of the science is being in general, the whole of it is predicated of those things which are separate from matter both in their intelligible constitution and in being (esse). For it is not only those things which can never exist in matter that are said to be separable from matter in their intelligible constitution and in being, such as God and the intellectual substances, but also those things that can exist without matter, such as being in general. This could not be the case, however, if their being depended on matter…. It is called metaphysics inasmuch as it considers being and the attributes which naturally accompany being (for things which transcend the physical order are discovered by the process of analysis, as the more common is discovered after the less common)


Ens commune is immaterial to the extent that it names that aspect of things that is not strictly identifiable with materiality, although every material thing may be considered as having this aspect. Ens commune is immaterial insofar as within its designation fall all things, material and immaterial, yet it is not the consideration of these things in their materiality or immateriality respectively. As Aquinas puts it in his commentary on Boethius’ De Trinitate,

something can exist separate from matter and motion … because by its nature it does not exist in matter and motion; but it can exist without them, though we sometimes find it with them”

In Librum Boethii De Trinitate, Question 5, Article 4, Bruno Decker, ed., (Leiden: E. J. Brill, 1965); English translation: The Division and Method of the Sciences, Armand Maurer, C.S.B., trans. (Toronto: Pontifical Institute of Mediaeval Studies, 1963), p. 45.

And that which is separate from matter in this sense is the subject matter of metaphysics.

So, while the subject matter of metaphysics, ens commune, is immaterial, it is a negative immateriality, i.e. it is the immateriality of considering all things, even material things, apart from any consideration of materiality as such. God and the angels can only be considered apart from matter since they are positively immaterial, but material things can be viewed both with regard to their material constitution, i.e. insofar as they move and change and are made of stuff, and with regard to their being, or unity, or act.

What is essential to metaphysics is its subject matter. As Aquinas expounds on this subject matter, ens commune, it is negatively immaterial. Ens commune as the subject of metaphysics must be negatively immaterial for two reasons (or for one reason viewed from two perspectives). First, being qua being is a formality under which one may consider things that is different from the formality of materiality. Thus, in order to do metaphysics, one must gain a perspective on all things, even material things, that is itself not a material perspective; one must view the world with an eye toward being. The second reason that the subject of metaphysics must be negatively immaterial is that metaphysics is a science distinct from physics. The metaphysician must know being as distinct from materiality because this science which he is endeavoring to undertake, metaphysics, is distinct from that science, natural philosophy, which is the study of things as material.

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