The Obsession With Essence and Necessity Began With Aristotle

The ancient and historically important philosophical notions of essence and necessity were vital to Aristotle’s overall philosophy. And, ever since Aristotle’s day, these philosophical notions have played a vital role in Western philosophy, theology, science and even in political theory.

It’s commonly agreed that the notion of essence began with Aristotle. However, a philosophical prototype can also be found in, for example, Plato’s Euthyphro. In that book Plato argued that physical entities acquire their essential being when they instantiate (or exemplify) what he called Forms. For Plato this meant that Forms are abstract universals which exist before any (concrete) particulars instantiate them. Plato therefore saw Forms as the paradigms of the particulars (i.e., things) which we experience in everyday life.

Aristotle himself departed from Plato in that he attempted to discover the (non-capitalised) form (or nucleus) of an individual physical entity. (Aristotle called such a thing ousia or substance.) In other words, Aristotle believed that Forms (or universals) must be instantiated in order to have being.

In more detail.

Aristotle used the Greek phrase τὸ τί ἦν εἶναι; which means “the what it was [or is] to be”. (The equivalent scholastic term is quiddity.) He also used the shorter phrase τὸ τί ἐστι; which means “the what it is”. (This is equivalent to the scholastic term haecceity). Then, in turn, these Greek phrases were rendered into the Latin term essentia (i.e., “essence”).

More relevantly to the following piece: Aristotle believed that gaining knowledge about the world is essentially about discovering what is essential and necessary to any given x.

The Purpose and Natural Place of Flames

Firstly, let’s take the often-cited example of Aristotle’s explanation of why fire (or flames) goes upwards. This is Aristotle on the subject:

“The ‘simple’ bodies, since they are four, fall into two pairs which belong to the two regions, each to each: for Fire and Air are forms of the body moving towards the ‘limit,’ while Earth and Water are forms of the body which moves towards the ‘centre’.”

Sure, it’s easy to be (retrospectively) smug about Aristotle’s views on fire and on much else. (Thus displaying a kind of Whig history of philosophy.) But, at the time, he had no reason not to conclude that flames displayed purposive behaviour. In addition, Aristotle relied on observations to come to his conclusions. After all, all flames do indeed move upwards. So, unlike Plato, Aristotle did pay much attention to the transitory (physical) things around him.

So why did Aristotle believe that flames go upward?

Aristotle reasoned in terms of what he called first principles. In the particular case of fire (or flames), he believed that fire seeks it “natural place” above the earth. This also meant that Aristotle believed that flames must necessarily rise upward.

Aristotle also believed he could discover was the “final cause” of things. In the case of flames, that final cause is the end of their upward journey. More technically, Aristotle argued that the four elements rise or fall toward to their natural place. (More on what Aristotle meant by the words “natural place” can be found here.) They do so in the concentric layers which surround the center of the earth and which form the sublunary spheres. More relevantly, the natural place of fire is higher than that of air but below the innermost celestial sphere (which contains the Moon).

This is, of course, Aristotle’s teleological account of things. Thus the telos of flames is to rise upward toward the heavens. In that sense, flames display “purposive behaviour” — their purpose is to rise to the heavens.

Necessity and Essence

As just hinted at, necessity is built into many of Aristotle’s explanations.

In basic terms, Aristotle believed that given causes necessitate given effects.

So let’s take flames (or fire) again.

Aristotle would have argued that the flames under a pan necessarily boil the water in the pan. In contemporary terms, this relation between flames and the boiling water in a pan is one of causal determination.

To return to the opening theme of flames rising upward.

So why is it also necessary that flames flow upward? Aristotle believed that this is because the essence of flames is that they flow upward. More abstractly:

Is it necessary that x displays behaviour (or action) A because x instantiates essence E.

Of course there’s a danger of conflating (or confusing) essence and necessity here. Surely only a physical (or perhaps abstract) property can be essential to any given x, not a specific behaviour (or action) of x.

However, why can’t a specific behaviour (or action) be seen as a property — even an essential property — of x? This means that the meaning of the word “essence” is — at least partly — a definitional (or stipulational) matter. That is, the word “essence” doesn’t itself have an essential meaning (or definition).

So we can conclude by arguing the following position:

If any given x always behaves (or acts) in a specific way, then that behaviour (or action) can be seen as being essential to x.

We can also link essence to behaviour (i.e., rather than seeing a specific behaviour — or action — as itself being essential). In this sense, we can argue that x’s essence E (i.e., a single property or a set of properties) brings about behavior A.

All this can be summed up and and stated in the following way:

If x has essence E, then it must behave (or act) in way A.

Yet even if there is essence E of x, how does E itself bring about behaviour A? In other words, how does E necessitate A?

The question as to whether behaviour can be essential is also relevant when it comes to subatomic particles. The following discussion on particles also raises the point that the philosophical notion of essence can be jettisoned entirely.

Relationalism: Particles and Mass

Subatomic particles are almost entirely defined in terms of their “relational” properties: such as their interactions with fields, forces or with other particles. (See my ‘Carlo Rovelli’s Relational Quantum Mechanics’.) Even the mass and charge of particles can’t be defined as (what philosophers call) intrinsic properties in that they’re determined by each particle’s place within a quantum system (or systems). More technically, a particle’s mass is determined by its relation to fields, forces and to other particles. And charge is similarly relational (see here).

This is the philosopher James Ladyman on this subject. He writes:

“[A] particle that never interacts with anything else could [never] have any value whatever for its mass.”


“since real particles will always interact with something or other [we can] ignore this”.

It can also be said that mass is “defined operationally” in that “the ratio of the masses of two particles is a constant of proportionality”. This too is a broader way of putting the better-known example which states that the number of electrons in an atom is equal to the number of protons. (Technically, a proton has a positive charge equal in magnitude to a unit of electron charge.)

Interestingly enough, Ladyman takes a particle’s lack of a (non-relational) essence to have the consequence that it can’t be what philosophers call an “individual”. (In broad terms, an individual is any given x which is deemed to be — to a large degree at least — self-sufficient, determinate and circumscribed.)

But firstly we need to see what this position is a reaction against. It’s largely a reaction against Leibniz. This is how Leibniz expressed his position on an individual

“The nature of an individual substance or of a complete being is to have a notion so complete that it is sufficient to contain and to allow us to deduce from it all the predicates of the subject to which this notion is attributed.”

On the other hand, James Ladyman and Don Ross — in relation to the physicist David Bohm’s position - say that

“[s]ince none of the physical properties ascribed to the particle will actually inhere in points of the trajectory, giving content to the claim that there is actually a ‘particle’ there would seem to require some notion of the raw stuff of the particle; in other words haecceities seem to be needed for the individuality of particles of Bohm theory too”.

The Irish philosopher Ernan McMullin also elaborated on this overall “relationist” position. He wrote:

“The use of namelike terms, such as ‘electron’, and the apparent causal simplicity of oil-drop or cloud-track experiments, could easily mislead one into supposing that electrons are very small localized individual entities with the standard mechanical properties of mass and momentum. Yet a bound electron might more accurately be thought of as a state of the system in which it is is bound than a separate discriminable entity… What is meant by ‘particle’ in this instance reduces to the expression of a force characteristic of a particular field[].”

Intuitive Knowledge of Essence and Necessity

We can now ask the following question:

How did Aristotle know about any given x’s essence or what is necessary about x’s behaviour?

An essence can’t be observed. And even if what is taken to be an essence could be observed, then that mere observation couldn’t tell a philosopher that such a property is essential. Properties don’t (as it were) broadcast their essential nature.

This meant that Aristotle couldn’t extract anything essential or necessary from flames (or any other given x) merely by observing them. Yet a similarly thing can be said about Isaac Newton and his discovery of the laws of gravity. In this case, too, Newton needed more than his apocryphal observation of a falling apple to conclude that it is gravity which accounts for such a thing. Newton also needed mathematical and theoretical insight — none of which could be drawn solely from his observations.

Of course Aristotle himself would never have claimed that essences can be observed. Instead, essences are known through intuition.

(It can be questioned whether the word “intuition” is an accurate translation of anything Aristotle actually wrote. The word itself comes from the Medieval Latin intuitio; which can be translated as: a looking at, [an] immediate cognition”.)

In the limited respect of his commitment to intuition, Aristotle was a Platonist.

Aristotle believed that intuition allows us to know (or “see”) things directly. That is, intuition allows us to make philosophical conclusions which go beyond observation, data or inductive support. However, unlike Plato, observation was still part of the overall story for Aristotle.

But what exactly is (philosophical) intuition?

Firstly, let’s ask the following question:

If we have direct access to the essence of any given x, then what would show the (philosophical) intuitor that he is wrong (or right) about what he concludes about x?

Interestingly enough, Aristotle is at one with those contemporary mathematical Platonists who similarly stress intuition. (See my ‘Platonist Roger Penrose Sees Mathematical Truths’.) Mathematical Platonists also claim to intuit (or “see”) those mathematical truths which haven’t — as yet — been proved.

So now, in turn, we can ask such a mathematician this question:

How do you know that some mathematical statements are true when they haven’t been proven to be true?


What w/could tell you that you’ve made a mistake about a mathematical statement’s truth?

And now to move back to Aristotle:

What is it, exactly, to intuit the essence of any given x or to intuit the necessary causes (or behavior) of any given x?

It may now seem that Aristotle’s position can be seen as an example of “a priori theorising” or rationalist reasoning. Yet Aristotle’s approach could never have been completely rationalist because he did, after all, take pains to observe such things as flames and he meticulously noted how they behaved.


To finish: it’s now worthwhile noting that Aristotle’s positions on essence and necessity are opposed to what occurred during — and after — what came to be called “the scientific revolution”.

More clearly, most scientists came to disregard the search for necessary truths completely. In terms of essence, what became important was not essence; but the motions of objects and the particles which constitute them. In addition, qualitative (or subjective) descriptions were substituted with quantitative descriptions. The search for “final causes” was also largely abandoned and scientists concentrated instead on finding (still to use Aristotelian terms) “efficient” material causes. Finally, although Aristotle relied to some degree on observations (as stated above), he didn’t carry out any experiments.

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