Philosophy 100 - 6.1.2 Ontological Perspectives on Substance

Up until now, this chapter has examined substance from a materialistic perspective—the concrete substances (water, fire, atoms) that make up the physical world that we see around us. As such, the discussion has been located squarely within a physicalism, an approach that equates the real world with the physical world. The study of existence, of being, of what is real—a discipline known as ontology—is broader. Ontos is the Greek participle from the verb “to be” and means “being.” What qualifies as being? How should we categorize being?


Naturalism, in its simplest form, is the view that meaningful inquiry includes only the physical and the laws governing physical entities and rejects the priority placed on reason assumed within metaphysics. For example, naturalism asserts that the inventory of beings allowed should include beings that are found within the physical realm. If we can see a thing or if we can test a thing within a laboratory environment, then a naturalist would include the being within their inventory. Naturalists also weed out the assumptions, theories, and questions that are introduced but are not capable of empirical proof.

The image depicts a printing of a wood engraving in which a man crawls under the edge of the sky, depicted as if it were a solid hemisphere, to look at the mysterious cosmos beyond.
Figure 6.3 This engraving first appeared on Camille Flammarion’s L’atmosphère: météorologie populaire (1888). It suggests that even the heavens (above or beyond the visible world) consist of mechanisms and regularities that could be discovered by scientific investigation. This is the essence of classical naturalism. (credit: Camille Flammarion/Wikipedia, public domain)

The debate between supernaturalism (that accepts the existence of beings beyond or above our natural realm) and naturalism is as old as philosophical inquiry itself. But the tension became particularly relevant during the modern period. During modernity, scholars made advances across many disciplines based upon a turn to a scientific method and a rejection of a priori reasoning.


The chapter on logic and reasoning covers the topic of logic in greater detail.

The Allegory of the Cave

In Book VII of The Republic, Plato offered his allegory of the cave, which depicts prisoners who have mistaken shadows cast on the wall of the cave for real beings and therefore have mistaken illusion for truth. The prisoners have been imprisoned throughout their lives. They are chained in place and have been positioned so that they can only see shadows that are cast upon the wall in front of them. They have come to treat the shadows not as the reflections that they are, but as something real. In an unexpected plot twist, one prisoner escapes and reaches the cave entrance. There, for the first time, he sees the sun—the true source of light (knowledge). After adjusting to the overpowering light emanating from the sun, the prisoner realizes that a fire was causing objects to cast shadows on the cave wall. The shadows cast by the fire within the cave were reflections. He realized that the shadows are not actual being or truth—they were merely fading facsimiles of reality. The escaped prisoner, freed from the chains of his earlier captivity (metaphorically speaking), understands the true nature of being and truth. He returns to the cave to “free” his fellow captives, but his claim is rejected by those in chains.

An illustration shows prisoners chained together behind a wall in a cave. Behind the wall is a fire, and between the fire and the wall are people carrying cutouts of a horse, a soldier, and a dog. The fire casts a large shadow of these images onto the wall near the prisoners.
Figure 6.4 The Allegory of the Cave (attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Plato’s Notion of Substance and Form

The prisoners were mistaking shadows for that which was real. But shadows do not last. As soon as the source of light fades, the shadows too disappear. If we want to identify the really real, Plato argued, we need to go beyond mere shadows and try to find those beings whose reality is not temporary. The idea or form of a thing, unlike the material “shadow,” was not subject to atrophy and change.

The Latin term substantia, translated as “substance,” describes the basic reality or essence of a thing that supports or stands under features that are incidental to the substance itself. While the so-called incidental features (e.g., quantity, time, place, etc.) can change, the essence of the entity endures. To account for the fundamental whatness of a thing, Plato posited an unchanging form or idea as the underlying and unchanging substance. As all things within a person’s reality are subject to change, Plato reasoned that the forms or unchanging basic realities concerning all things must not be located within this world. He therefore posited a realm in which change did not occur.

There is an intuitive appeal to Plato’s accounting of the real to forms. How else could we explain our ability to recognize a type of being given the sheer number of differences we will observe in the instances of a thing? We can make sense of dog, for example, because beyond the differences found among spaniels, poodles, and retrievers, there is a form of dog that accounts for knowing dog and being as dog.

Aristotle on Matter and Form

Aristotle, a student of Plato, disagreed with his teacher. If forms did exist, he challenged, then how could forms influence things? How could an immaterial form–which lacks matter—cause change to material entities?

In addition, what about concepts that are not easily reducible to a simple meaning or idea? Aristotle noted that “good was said in many ways” (Ethics 1096a–b as found in Adamson 2016, 232). The reduction to a single form to identify the whatness for something works when the concept is simple but does not work when a wide-ranging concept (such as “the good”) is considered. Aristotle agreed with the approach of isolating dogness as the essence, but through the study of specific instances or particulars. He encouraged natural observation of the entity in question and introduced the categories of species and genera.

Unlike Plato, Aristotle does not posit an otherworldly form or collection of forms. In his middle and later works, Aristotle explained substance through a composite of matter and form. Form, much like an idea a sculptor has in mind, is the unchanging purpose or whatness informing each particular or individual instance. In this case of a sculpture, the sculptor’s vision or idea was referred to as the formal cause. The marble would be the material cause. The ability and artistic skill of the sculptor was termed the efficient cause. The final cause reflected the purpose of the being, or the reason why the sculpture was made in the first place.

The idea of substance being a composite of form within matter became known as hylomorphism. The Greek word hyle translates as “wood.” Here wood is figurative, a symbol of basic building material that is shaped by the form within a particular instance. The form does not reside in the Platonic heavens but, through purpose and efficiency, moves a particular thing from its beginning state (potentiality) along a continuum toward its final goal (actuality). The acorn is driven by its form and purpose to become the mighty oak. The movement from potentiality to actuality requires material and the efficient (proper) application of these materials such that the acorn can become!

The painting School of Athens shows a gathering of ancient people. They are gathered together in different groups, surrounded by stone arches and statues.
Figure 6.5 School of Athens (credit: modification of work “The School of Athens by Raphael” by Bradley Weber/Flickr, CC BY 2.0)

The attitudes of Plato and Aristotle are reflected in Figure 6.5. The School of Athens was discussed in the introduction to philosophy chapter. This section details the interaction between the two central characters in the fresco painting. Plato is the subject displayed to the left of center, and Aristotle is the subject depicted to the right of center. Plato’s gesture toward the heavens with his right hand was the artist’s way of recognizing Plato’s theory of forms. For Plato, forms were immutable and the ultimate reality. Forms were supposed to exist outside of our earthly realm as the things we observe are subject to change. Aristotle’s gesture with his right hand was the artist’s representation of Aristotle’s stressing of the form embedded within particular matter. The ultimate reality was supposed to be within each instance of matter observed. The material components were subject to change, but the form was not.

What do you think? The crucial difference introduced at this historical point was the emphasis placed upon particulars—individual instances of an entity—by Aristotle. While Plato stressed forms and asserted that there could be no individual instance without the form, Aristotle stressed particulars and asserted that without individual instances, there could be no knowledge of the form. Whereas Plato holds that beauty itself causes the beauty we see in flowers or faces, Aristotle asserts that there is no such thing as beauty without beautiful things, such as flowers and faces (Adamson, 2016, p. 231).


Listen to the podcast “Aristotle on Substance” in the series The History of Philosophy without Any Gaps.

The content of this course has been taken from the free Philosophy textbook by Openstax