“If the eye were an animal, sight would be its soul; for this is the eye’s substance – that corresponds to its principle. The eye is a matter for sight, and if this fails it is no longer an eye, except homonymously, just like an eye in stone or a painted eye.”
- Aristotle, On the Soul, Pg. 166
By ‘substance’, Aristotle means what a thing is, its being. In Categories, Aristotle defines a primary substance as an individual thing, such as an individual man, and secondary substances as species, such as men, as well as genera, such as animals. In Metaphysics he defines substance as essence, or what it is to be a particular thing, meaning the form, and not the matter; though in On the Soul he defines substance as a composite of matter and form.
By ‘principle’, Aristotle means what a thing is for. He uses the example of the principle of a house being for protection from the elements.
Substance here is the form of an eye. Eyes consist of a compound of matter and form. The purpose of eyes is to see, and the soul, the sight, is what enables it to do that. If the soul were to leave the eye, or animal, then the eye would no longer be able to see. Its purpose then gone, it would no longer be an eye, for the purpose of the eye is to see. It would be called an eye in name only. For Aristotle, things are deprived of being when deprived of form (Physics I).
This argument brings up questions which Aristotle does not answer. Extending the eye/sight analogy to the souls of animals and humans, he determines their purpose to be to reproduce. He does not address the issue of those who cannot or choose not to reproduce, whether he believes them to have souls that are defective or otherwise lacking, or if these individuals are then animals or humans in name only. In Categories, Aristotle says that a substance does not admit of more or less, that is one substance is not more or less of a substance than another substance, so it would follow that if an individual does
not reproduce, he or she might not have a soul, rather than having less of a soul than a reproducing individual.
Aristotle sees form as actuality and matter as potentiality, both being present in a body, with soul being the actuality of the body. Sight here would be the actuality of the eye.
The quote’s purpose in On the Soul is to serve as an analogy to the soul proper, to demonstrate the causes and purpose of the soul. It incorporates the ideas of substance, form, matter, cause, purpose, like/unlike, and homonymy.
Applying Aristotle’s four causes to the eye analogy:
1. the material cause of an eye would be the matter, or tissue, of the eye
2. the formal cause would be what it is to be an eye: the eye is an organ for sight
3. the efficient cause of an eye would be the father of the eye
4. the final cause would be sight: the purpose of an eye is to see
The eye is an organ for sight; if it cannot see, then it is no longer an eye, for it fails in the form department. If an eye’s purpose no longer exists, it is no longer an eye, for an eye’s end is to see. As in other cases, the formal and efficient causes are the same. An eye with only a material cause is what Aristotle calls an eye in name only (homonymously). The efficient cause of an eye as animal would be an eye, for presumably the eye’s (animal’s) father is an eye, and it is the father, which contributes form to offspring.
Aristotle’s analogy is used to explain the nature of the soul and it’s relation to the body. The eye, he says, is only an eye if it fulfills its purpose by having the ability of sight. In the same way, the body is only such if it has a soul. The soul is less a literal thing than it is the fulfilling of the potential for being.
The exception to this is an image of an eye or body, or an eye or body that no longer has sight or a soul. In these cases that same eye that once had the ability of sight is still an eye, but in name alone, for the eye is no longer fulfilling its potential.
Another way to look at these objects, the body and the eye, is as potentiality bodies. Bodies that have a soul and eyes that have sight are fulfilling their potential. The soul is simply the purpose, the reason, and the potential of the body. It is something that every
body has the capacity for, but not all will have. This is not to say, however, that the soul can exist without the body. For, by analogy, can one have sight without an eye? The soul itself does not exist, but is better represented as a quality of the living body or seeing eye.
One could also see this as Aristotle’s version of Plato’s forms. The form equates to the soul or potential it is the ideal, the possibility. In the forms, we saw that the ideal form was at the top, with everything else being a representation or shadow of it. Here the order is reversed: the matter already exists, and what emerges from it is the fulfilling of its potential. The body without a soul is simply matter, but a body that also fulfills its potential by having a soul is more than just matter. Aristotle compared to Plato: Plato is notorious for his association of art (images, etc) with lowest grade of reality, or that which is furthest removed from being in participation with the forms. Fortunately for the “shadows” (Allegory of the Cave), problems that raised in Parmenides (Third Man Argument) combined with Aristotle’s criticism of Plato’s ontology resulted in a new metaphysic which effectively refuted the principle source of this Platonic prejudice. With the help of the early chapters of Categories, this passage in particular illustrates Aristotle’s criticism.
In the first sentence of the first paragraph of the first chapter of Categories, Aristotle defined a homonymous relationship between words as one “when things have only a name in common and the definition of being which corresponds to the name is different…Thus, for example, both a man and a picture (of a man) are animals.” Here, Aristotle is acknowledging a linguistic similarity between words that Plato’s theory of forms cannot consent to. For Plato, a man and a picture of man cannot be equally animal due to the fact that they are inextricably on two separate grades of reality (which grades of reality become confusing when contrasting the double-divided line [4 grades of reality], with the allegory of the cave [3 grades of reality]. At this point it suffices to acknowledge that where exactly “man” and “a picture (of a man)” fit in the conflicting Platonic paradigms is less important than the fact that they are in no way equal with respect to their participation in the forms). Due to the fact that Aristotle only articulates
the potential and the actual in his ontology, he has only a single grade of reality and can simply acknowledge the homonymous relationship that all words of the same name, but opposing definitions share. Thus, with the theory of forms no longer estranging the entire realm of arts and images from grades of reality, Aristotle instantly revived from subordination the arts, images, and imagination (etc…) that took a thrashing at the hands of Plato in the Republic. Evidence Aristotle intended such a revival is hinted at by the uses of the words “an eye in a stone or a painted eye” in the passage. While an “eye in a stone” need not be interpreted as referring to art, a “painted eye” seems to explicitly refer to the hand of an artist. No longer was a painting, or an image a mere copy, desiring to be one with its respective form. Now, all individual objects are subject to their position in the Great Chain of Being. Aristotle Compared to Bruno: When Aristotle says, "For if the eye were an animal, sight would be its soul;" he implies that animals have souls but not parts of animals. This coincides with his belief that the soul is the form of a natural body that has the potentiality of life, which, by definition, includes self-nourishment, growth and decay. Thus Aristotle does not believe that the eye has a soul. To Aristotle, the soul is an aspect confined to things which have abodies and seem to animate. In Aristotle's eyes, life and soul exist only at certain points, here where there is a person or where there is a plant. This is the point of difference when compared to the ideas of Bruno.
Bruno's belief in a world-soul causes him to see life in the world as a voice would exist in a room: everywhere at all times. Bruno says that all things have the "essentials of life" not just natural bodies. When confronted with his own belief he adds that if something is not perceivably animate it is alive according to the primal being of animation of life" (15). Here we see Aristotle's idea of matter having potentiality applied to all things. It is a belief held by both philosophers in stages or states of life. However, according to Aristotle the soul animates a body and the body does not have life until this happens. According to Bruno, the body always has its soul and is always alive at least in the initial state of being. A way to look at this is to say that before the earth had any life
it was in its "primal state". Obviously life sprang up and now exists on earth. To Bruno, this demonstrates life in something that does not look animated.
In Aristotle's case of the eye failing then, Bruno would not say that the eye fails to be an eye. This is because he never takes part in the belief that the eye lost its soul. Rather Bruno exclaims, "I say that if life is found in all things, the soul must be the form of all things... And therefore such form is no less enduring than matter" (16). Here, Bruno says nothing can even exist without a soul; thus the eye could never lose its soul. Furthermore, because form will exist as long as matter does, the soul of the eye cannot disappear unless the physical eye disappears. This view allows Bruno to take his theory further. Because all things have soul but limited matter, there all sorts of combinations of things that will have a soul but without certain faculties. This accounts for anything that might be questionable, such as a virus. Bruno's argument stays constant no matter what object is in question.
Cohen, S. Marc, "Aristotle's Metaphysics", The Stanford Encyclopedia of Philosophy (Summer 2003 Edition), Edward N. Zalta (ed.), URL = .
Cohen, S. Marc, Lecture Notes Philosophy 320, University of Washington, URL =