April 22, 2026

 

Table of Contents

 

1. The Theory Itself

2. Teleology: Orderly & Intelligible Universe Via Inherent Ends

3. The Theory's Universality: Applying it to Difficult Cases

    a. Borderline Plant/Animal Life

    b. Supernatural Beings

    c. AI   

4. Universality Since No Specific Mind Is Tied to a Set Formula

5. Reference

 

What does it mean for something to have a mind? Fortunately, Aristotle provided us great insight.

 

In his work De Anima (On the Soul), he explains that something has a mind (i.e. soul, psyche) if it originates its essential activity. For example, an active volcano doesn't have a mind since its spewing lava doesn't originate from it but is a result of the Earth's forces underneath; it is merely like a spigot after a human turns on the water. Likewise, the essential activity of a knife is to cut but it can do this only if someone is wielding it. Thus, to him, minds exist only in the realm of living things. There is something to that, as things in the realm of inanimate matter have a completely deterministic, domino-like motion that goes against our basic notions of what a mind is.

 

As you'll see later, there's one more basic requirement for a being to have a mind. But before uncovering that, it helps to first learn the kinds of minds there are and what they do.

 

Aristotle identified three fundamental types of minds, distinguished by their radically different functions.

 

According to him, all living things have at least a nutritive soul. This includes powers such as the capacities for physical growth, repair, and reproduction. We'll call this the "plant soul," since it is most closely associated with plants and plant-like life.

 

In addition, all living things with locomotion have sense perception. Why? Because unlike plants and plant-like things, they don't get their nutrition directly from the earth or immediate environment but must seek and find it. Along with perception, such beings must have desire, passion, and wish, presumably because these are necessary for them to be driven to seek their nutrition and avoid various kinds of obstacles along the way. We'll call this set of capacities the "animal soul," obviously because of its closer association with what we call "animals."

 

Some things with an animal soul also have imagination (e.g. creatures that dream during sleep have this), but not the ability to think.

 

Finally, some things with sense perception and imagination also have reason and thus the power to think -- essentially, the capacity to acquire concepts from particular perceptions or imaginations that are alike. Naturally, we'll call this the "rational soul."

 

So, what Aristotle presented was a triple layer, one-way dependency: all beings with a rational soul must have an animal soul, and all beings with an animal soul must have a plant soul -- but not vice versa.

 

There's something else that plant, animal, and rational minds have in common that helps us realize that originative, essential action alone doesn't constitute a mind. He gives another key condition required for a mind to exist.

 

For example, a clock independently tells time. Sure, it needs an external energy source to get it going. But once that condition is in place, the time telling originates from the clock.....So, the clock has a mind.

 

Why does it not ring true that the clock has a mind? True, the mechanical, repetitive nature of its activity clashes against the spontaneity that seems indicative of genuine mental activity. But there's something even deeper. It's that its essential activity isn't based on a goal for itself but, rather, for another party (humans). Time telling doesn't in any way help the clock; it only helps the humans using it. It has no goal for itself. Therefore the clock doesn't have a mind but is merely a tool.

 

***

So, when something has a mind, it's not just that the entity's essential activity originates from it but also that the activity springs from its own goal rather than another's.

***

 

Obviously, "goal" doesn't have to mean a conscious one or one from a rational plan. Plants don't deliberately repair themselves and grow, but that doesn't make the goal behind those actions any less their own. Those internal activities are meant to help the individual plant and therefore they exist only for it.

 

All of these minds -- plant, animal, and rational -- benefit the entity possessing them. They exist for it, and therefore each has goals independent of any external source. Mainly, the plant soul benefits the entity's body. The animal soul helps it navigate the world both through locomotion, desire, and the senses. The rational soul allows it to understand the world, aiding both the plant and animal soul, but also creating the goal of thinking as an end in itself for the entity.

 

Thus we can think of Aristotle's notion of "goal" as synonymous with "function." Plant souls -- and the structures that comprise them -- have a certain function in helping the existence of the entity possessing them. The same is true of sense perception, desire, and other animal-soul attributes; as well as reason's concepts, whether innate or acquired.

 

An important implication of this is the assumption that the universe has a natural orderliness. Aristotle saw this in all of Nature, but especially in the world of living things; living things as having structures and capacities that exist for a purpose and not arbitrarily: "...Nature does nothing in vain. For all things that exist by Nature are means to an end, or will be concomitants of means to an end." (On the Soul, Book 3, Chapter 12).

 

So, we can understand things and their parts by asking what their purpose is. For example, some carnivores have certain anatomical features -- sharp teeth and maybe sharp claws too -- because carnivores' fundamental purpose, individually and in the collective ecosystem, is to hunt prey. Their ability to kill and eat prey is what allows them to live and ultimately to continue their species with offspring, thus explaining their features.

 

From this perspective, we needn't assume that a thing's purpose in Nature is based on some conscious plan or design from an external agent, but is simply based on its essence: what a thing is determines the ultimate end it can fulfill, and in turn, what end a thing can ultimately fulfill tells us what a thing is. For example, a carnivore isn't a carnivore because of what purpose someone intended it to have, but because of what it fundamentally does and can most effectively do. All animals can reproduce, sense their environment, etc, but what separates carnivores from others is how they make a living and their ability to make a living that way. Non-carnivores too can kill and eat flesh but not as effectively as true carnivores, just as a screwdriver "can" be used to hammer a nail. A carnivore is "most carnivore" when it is fulfilling its ultimate potential and thus actualizing its end: eating and digesting flesh.

 

This view that things in Nature each have an end that can be deduced by seeing their purpose is called "teleology."

 

As for conscious design, Aristotle did believe in an ultimate being -- "the first mover" -- behind all of the universe. But that's another issue. The teleological view can be taken by an agnostic or even an atheist, since it is simply an issue of seeing what the essence of a thing is. And, according to Aristotle's philosophical system, we can know what a thing is by seeing what it's fundamental activity is, thus knowing it's potential/end even when it's not engaged in that activity. But even if we take a neutral or skeptical view on God, a guiding assumption in teleology is that Nature has an orderliness and that things and their parts in Nature have a purpose.

 

Sure, there can be mishaps or anomalies. But in the vast majority of cases, certain abilities and structures in Nature exist for a purpose. For example, what if a creature had formidable teeth and claws, but no sense perception for finding prey or food -- like a plant -- or simply never a desire to seek prey. Aristotle would have found that puzzling and it's safe to say that sentiment would resonate with the great majority of biologists and those in related fields. The creature's plant soul would have evolved a carnivore physically but there wouldn't be a matching carnivore at the animal level of mind. It would be natural to wonder: what then is the point of those big, sharp teeth and claws? Thus most people intuitively gravitate to Aristotle's view of an orderly universe. For that reason, it's not unique to Aristotle in Western philosophy nor alien to Eastern philosophy, among others.

 

We can see that this assumption of natural orderliness is necessary in order for Aristotle's 3-way hiearchy of minds to make sense. Again, imagine a being that has a plant soul to manage its basic bodily needs, but then has an animal soul that either lacks sense perception or desire. The whole system would break down. Sense perception helps the animal seek its desires and, without desires, its sense perception would have no value. Nor would the plant soul ultimately have any value if desires didn't exist: the creature would be indifferent to its own bodily survival and well being. Thus the combination is complementary and necessary. So we assume that there will (almost always) be an orderliness that allows each type of mind to have purpose. Minds and their capacities within them will each have a function, and include other minds and capacities to fulfill their function if necessary.

 

Thus, from a teleological view, if an entity, structure, or process appears to serve no purpose, there's a good chance we're just not understanding its function.

 

Can Aristotle's theory of mind be trusted as a standard of measurement, setting reliable conditions for testing whether or not something has a mind, especially a rational mind?

 

In other words, do we have reason to believe that it holds up in all cases of minds, known or imagined?

 

Clearly we can't know all possible cases, so there will always be some uncertainty. But it helps to look at some of the more obvious cases that are difficult and unclear. If they pass the test, then it's reasonable to assume that all other cases probably do as well. These cases are: borderline plant/animal creatures, supernatural beings, and AI.

 

What's not problematic is his view that whatever has a mind originates its essential activity and that the activity serves the thing's own ends. Once a thing's essential activity springs from itself and for itself, it's no longer just some kind of tool or involved in the mechanistic processes of inanimate things that clearly lack any sort of mind. 

 

What is not immediately clear is whether the conditional relationships Aristotle gives between rational, animal, and plant minds are true in all possible cases. (Aristotle never claimed that they were true in all possible cases, but we can try to see if they are.)

 

Specifically, it is the conditional relationship between animal and plant minds, as well as which abilities necessarily exist in each of those minds and which cannot, that are the main sources of controversy -- at least when trying to see if these are eternal, metaphysical truths rather than just contingencies that are true (or mostly true) on Earth; or even the entire, actual Universe; but not necessarily in all possible worlds.

For, the second level of dependency Aristotle presents is clearly a necessary truth: the rational mind cannot exist without the animal mind. Concept formation requires particulars as the necessary "material" to make the universal. Put differently, if someone couldn't at least imagine an example when asked about what a concept is, would you say they had the concept? Maybe they couldn't clearly express an example due to limited vocabulary on the subject, but they should at least be able to imagine one. Having a concept without some underlying knowledge of what particulars it refers to is impossible -- at least for most concepts, those tying back to individual things and specific relationships. Perception and imagination provide the particulars. (See here, for the exceptions: innate concepts.)

 

So, we'll look at whether plant souls necessarily exist in supernatural beings and AI, and whether sense perception can exist in plants and need exist in animals.

Aristotle's distinction between plant and animal life is intuitive and a basic classification that most people use when it comes to living things. For example, we can all understand that even though things like bacteria, fungus, etc aren't "plants" in the strict biological sense, there is something they have in common with plants that separates them from things we call animals: mainly a lack of sense of perception -- an absence of concsiousness. That is the essential distinction between plants and animals, according to Aristotle: "...it is the possession of sensation that leads us for the first time to speak of living things as animals; for even those beings that possess no power of local movement but do possess the power of sensation we call animals and not merely living things." (Book 2, Chapter 2).

 

But Aristotle makes some other claims about animals, apart from their key attribute separating them from plants. If an animal does have locomotion, it necessarily has sensation. And any being with sensation necessarily has the capacity for pleasure and pain, and hence desire:

 

"Every body capable of forward movement would, if unendowed with sensation, perish and fail to reach its end, which is the aim of Nature; for how could it obtain nutriment?...Therefore no body which is not stationary has soul without sensation." (Book 3, Chapter 12).

 

And

 

"...now all animals have one sense at least, viz. touch, and whatever has a sense has the capacity for pleasant and painful objects present to it, and wherever these are present, there is desire, for desire is just appetition of what is pleasant." (Book 2, Chapter 3). 

 

All of this flows from Aristotle's view that Nature has an inherent orderliness. It doesn't create capacities and structures in living things without those serving some usefulness and purpose for those things. Thus we should expect one ability to be present if another ability could not be useful without it. So, adding to the quote above, we can rephrase a previous point: what good would sense perception be if a being had no desire to follow the pleasures and avoid the pains that its senses provided?

 

Still, does Aristotle's entire picture of animals hold up?

 

Some creatures aren't clearly either plant or animal, having only some of the key features of animals that both biology and Aristotle's theory recognizes. For example, many one-celled creatures are mobile (e.g. amoeba, paramecium, euglena), and therefore would necessarily have sense perception, according to Aristotle. But it's a stretch to say that they have true sense perception, even though they have perception processes similar to it. Moreover, they don't have a nervous system and therefore can't feel pleasure or pain. Since sensation entails the capacity for pleasure and pain, in Aristotle's view, then lacking that capacity would indicate that they don't have true sense perception. At least if we stay true to Aristotle's picture.

 

But we can't deny that they have locomotion. So, these are creatures with a knowledge process similar to that of plants and yet, unlike plants, are mobile. They are like mobile plant life, perhaps a necessary bridge between plant life and animals. These are legitimate counterexamples to at least part of Aristotle's theory.

 

Also, because all creatures with locomation have sense perception, and sense perception is the distinguishing feature of animals, then Aristotle believed that all mobile creatures are animals.

 

So, there's no way to counter these counterexamples. Either some animals don't have sense perception: there are mobile things without pleasure/pain capacity and thus sense lacking perception. Or some plants do have it: there are mobile things, which thereby have sense perception, but lack pleasure/pain capacity and therefore aren't animals.

 

It's important to make clear that Aristotle was claiming only that creatures with locomotion must have sensation and not vice versa. To quote him again: "...even those beings that possess no power of local movement but do possess the power of sensation we call animals and not merely living things." Adult oysters and mussels are two familiar examples. So at least those cases aren't a problem for his theory.

 

Nevertheless, the counterexamples above are relatively superficial and don't do any real damage to Aristotle's theory of mind. This is because the plant/animal distinction and hiearchy still holds at a basic metaphysical level.

Suppose we find that all living things necessarily have sense perception. That would mean that the things we call plants and plant-like life are essentially animals and therefore the plant/animal distinction is false -- at the level of living entities. But within each of those things we call plants and animals would still exist two different kinds of mind: the plant and the animal. This is because the activities of the plant soul and that of the animal soul are entirely different. The plant soul deals with the issues of the physical body whereas the animal soul pertains to consciousness of individual objects, whether external or internal.

 

So, there would still be a metaphysical difference between plant minds and animal minds, even though all living things would at least be animals essentially, and something more if they had the ability to reason. The terms "plant soul" and "animal soul" would still be useful too, since the capacities associated with plant souls are best expressed in things we call "plants" and "plant-like life," while sense perception is best expressed in things we call "animals."

That animal souls depend on plant souls to exist isn't as clearly an absolute as that rational souls depend on animal souls. But it definitely has wider application than just to the biological world.

 

Aristotle hesitated to attach that requirement to divine beings: "This power of self-nutrition can be isolated from the other powers mentioned, but not they from it -- in mortal beings at least." (Book 2, Chapter 2).

 

But it's a testament to his theory that, actually, gods and other supernatural beings would necessarily have some type of plant soul. This opens the door for the theory applying not just to all existing or known minds, but to all possible minds. And if not, it at least means that it applies to more than just life in the natural world, possibly including AI.

 

There are two key reasons that gods too must have a plant soul. At least this would be true of gods as commonly understood: immortal personalities or beings that are nevertheless not the entire universe.

 

First, gods would need a body. Again, conceptual understanding requires mental particulars. Knowledge of such things can only happen through a viewpoint/lense of limited space time and space, otherwise no particulars could be captured. Thus gods would need a limited body -- something to contain their consciousness within time and space. The possibility of movement (including mental action), whether on an earthly realm or some other, also requires a unit of limited time and space. Otherwise, the thing moving would always "be there" and real movement from one point to another could not happen.

 

Secondly, their immortality would not be possible unless their body had a plant soul. Inanimate objects are not inherently everlasting and stay in tact or without any damage only accidentally. Material gives an object a form, a  presence, in space and time. But it does not itself grow, repair, or maintain that form. By definition, it lacks such capacities. Even "self-healing" materials naturally lose that property over time. Material that could maintain an object's form forever or regenerate whenever the object comprised of it is damaged would reveal plant soul capacities; it would have an intelligence ("magic") behind it. Therefore gods' immortality wouldn't be because their bodies have a heavenly material with special material properties.

 

So, it could be said that gods would have the ultimate plant soul. At minimum, they could maintain their astral body for eternity, which is to say that they could maintain its form forever. Maybe the maintainence would be based on sheer will, but that their will could accomplish those things specific to the body would nevertheless show plant soul powers.

What about AI? There are of course debates over whether AI truly thinks and even whether it has a mind at all. Let's just assume for now that both of those are true.

 

So, would it necessarily have a plant mind at its base? Definitely it would need at least some of the same plant-soul capacities found in biological entities. Take, for instance, a chess bot. The electrical circuitry of the computer hardware provides it the necessary "nutrient," electricity, for it to actually play chess. And even though a chess bot could exist without being able to create new copies of itself, if it were to produce new copies then it would need supporting software to do that. Thus the supporting software would serve the same function as structures in the biological world that allow for reproduction.

 

But, at a bare minimum, for the rational processes of the bot to occur at all, the electric circuity is the key requirement.

 

And just for good measure, what about the rational-animal mind relationship? Any type of AI needs input in order to calculate. So the software and hardware structures allowing the input function in the same way that sense perception does. Sticking with our example, basic chess bots -- not advanced ones with cameras that actually look at the physical board -- have 1D consciousness and would need some form of time consciousness to calculate moves. (See here.) It is spatio-temporal consciousness that we associate with animal minds.

 

So, even though chess bots are neither biological nor supernatural entities, nevertheless the same basic metaphysical mind-structure exists for them as for the other two. We can say the same for other AI.

 

The previous section shows we don't need to adopt a strict interpretation of Aristotle's theory of mind (i.e. confined to how such minds are expressed in Nature) in order to apply it to AI. Reduced to its bare minimum, Aristotle's theory of mind is simply this: something has a mind if it has at least one self-sufficient capacity of activity and that activity is a goal for itself.

 

Gods by definition, or at least most people's definition, are immortal. Many other qualities often attributed to them are up for debate. We don't have to assume they have or need the capacities of processing nutrients or reproducing things of their kind, as with life in the natural world. By general definition, their plant soul would only need capacities such as bodily repair or maintenance.

 

Likewise, the set of capacities and nature of a plant's plant soul is different from that of the human's plant soul in the body. The set of animal soul capacities of an earth worm are different from those of a bear. We can assume that the set of rational capacities in at least most examples of AI are different -- more limited -- than those of a human. 

 

Aristotle was clearly aware of this need for intellectual flexibility when trying  to understand the respective soul kinds of different kinds of beings. As he said in Book 2, Chapter 3: "It is evident that the way to give [the most adequate] definition of soul is to seek in the case of each of its forms for the most appropriate definition." (Brackets mine.)

 

The statement was in reference to the general kinds of souls. But the same point can also apply to any of the species under them. The real takeaway is  that a thing can still have a plant, animal, or rational mind even if its respective set of capacities don't match  those of another entity possessing the same kind of mind in question. So, Aristotle's classification still holds even when there are significant differences between the sets.

 

All quotes are from the following work:

Richard McKeon, The Basic Works of Aristotle (New York: Random House, 1941).