Within his Essay Concerning Human Understanding, Locke picks up where his predecessors in epistemological theorizing left off and proceeds to shift the study towards a more empiricist approach. Amongst the complexities of his theory, the notions of ‘substance’, ‘nominal essence’ and ‘real essence’ are fundamental and relate, in Locke’s view, to explain the nature of the things that we perceive. In this essay, I will aim to explain the theory which binds these three concepts together and, in turn, examine their role in the overall framework. As is often the case with early philosophical works, however, we find opposing interpretations of his meaning amongst commentators; I shall endeavor to examine the points of contention and, ultimately, give an account of what seems to be the natural reading.
To begin with, I would like to consider Locke’s conception of ‘substance.’ Locke provides us with two levels at which we can talk of substance; at the general level ( the ‘notion of pure substance in general (Locke, An Essay Concerning Human Understanding, II. XXIII, 2)) and at the level of particulars or individual things (‘ideas of particular sorts of substance.’ (ibid, II, XXIII, 3)) Aside from this simply asserted distinction within the Essay, however, the remainder of Locke’s conception of substance is controversial and much debated. The way in which it at first appears in the Essay, and the way in which Locke’s view was traditionally interpreted, is that he conceives of substance as acting in a supporting role; the qualities or properties which an object possesses, both at a constitutional level and at an observable level, must be anchored by something. The properties which come together to form an object cannot simply exist as a collection of properties, they must be bound to something which Locke calls a ‘substratum.’ This substratum would be, essentially, property-less. As Locke explains, ‘ The idea then we have, to which we give the general name substance, being nothing, but the supposed, but unknown support of those qualities, we find existing, which we imagine cannot subsist, sine re substante, without something to support them, we call that support substantia, which, according to the true import of the word, is in plain English, standing under or upholding. ‘ (ibid. II, XXIII, 2)
It is open to debate how Locke actually views this unknowable substance which supposedly anchors all qualities; Ayers puts the problem succinctly: ‘the question is this: does Locke think of the ‘substance’ or ‘substratum’ of observable properties as an entity distinct from all its properties?’ or ‘is the unknown ‘substance’ or ‘substratum’ nothing over and above the unknown ‘real essence’?’ (M. Ayers ‘The Ideas of Power and Substance in Locke’s Philosophy’ in I. Tipton (ed.), p.77) It seems that either interpretation causes problems for Locke; if he wishes to maintain that the substratum does exist as distinct from all qualities, can it really be said to be anything at all? ‘How is an utterly featureless ‘something’ different from nothing at all?’ (E.J. Lowe Locke on Human Understanding ch.4, p.75) Conversely, however, if the substratum were not distinct from properties, it would have properties of its own which, according to Locke’s framework, would require anchoring or support.( ibid.) Scholars have suggested numerous ways of supporting the idea that Locke viewed ‘real essence’ as basically interchangeable with ‘substance.’ Lowe, for example, suggests that Locke may be using the notion of substance as a name for the basic microstructure of objects: ‘recalling…Locke’s sympathy for atomism, might we not suppose that what he understands by the ‘substratum’ of a macroscopic object like a tree is the complex, organised assembly of material atoms that are its ultimate substantial constituents- what he elsewhere calls the ‘real essence” (ibid.) An interpretation like this arguably can find textual support; Locke talks of simple ideas flowing ‘from the particular internal Constitution, or unknown Essence of that substance.’ (Locke, An Essay Concerning Human Understanding, II, XXIII,3) The conjunction ‘or’ here suggests an equality and interchangeability of the two notions. However, we cannot simply rely on grammatical nuances to establish a solid interpretation of Locke; it seems that if Locke were to hold that the substratum were not simply a way of expressing the constitution of an object, he would be adhering to the Aristotelian notion of ‘prime matter’ which, taking into account the philosophical climate in which Locke was writing, might have been embarrassing. As Ayers maintains, ‘it is improbable to the point of impossibility that Locke, who is an anti-Aristotelian corpuscularian of the school of Boyle, should himself, using the very term substratum, advance a view so analogous to what Berkeley describes as ‘that antiquated and so much ridiculed notion of materia prima to be met with in Aristotle and his followers.’ (M. Ayers ‘The Ideas of Power and Substance in Locke’s Philosophy’ in I. Tipton (ed.), p.78) Locke does seem to talk of a characterless substratum in a rather derogatory way: ‘ They who first ran into the Notion of Accidents, as a sort of real Beings, that needed something to inhere in, were forced to find out the word Substance, to support them. Had the poor Indian Philosopher (who imagined that the Earth also wanted something to bear it up) but thought of this word Substance, he needed not to have been at the trouble to find an elephant to support it, and a Tortoise to support his Elephant: The word Substance would have done it effectually.’ (Locke, An Essay Concerning Human Understanding, II, XIII, 19) It could be, however, that this comparison is simply indicating the level at which substance is unknowable.
As much as we might wish to claim that Locke was not inconsistent with his own rejection of Aristotelian prime matter and that of his contemporaries, we cannot deny that it does seem that way. Locke frequently reinforces the need for something to support qualities: ‘…we cannot conceive, how they should subsist alone.'(Locke, An Essay Concerning Human Understanding, II, XXIII, 4) And, as mentioned previously, something intended to support qualities cannot have qualities of its own which require support. If substance was basically equatable to real essence or to the constitution of objects at an atomic level, surely Locke would have made this more explicit. There is an undeniable distinction being made. As Lowe points out, the distinction is necessary for Locke’s theory; the substratum has a ‘metaphysical role to play above and beyond any merely scientific explanatory role which could be offered by the doctrine of atomism.’ (E.J. Lowe Locke on Human Understanding ch.4, p.76) The atoms themselves have qualities and properties which require supporting. Therefore, it seems to me that the most obvious reading is one in which Locke is espousing the idea of a supportive, characterless, underlying substance. Though this is contested, however, it is undeniable that whatever Locke is attempting to convey by talking of substance, this substance is entirely unknowable.
According to Locke, substances have two essences- their real essence and their nominal essence; this recognition of two distinct essences is crucial for the way in which Locke constructs his theory of how we come to classify objects. Locke defines ‘real essence’ as that which exists at the level of constitution; a substance’s real essence is what causes the qualities we can observe but the real essence itself is unobservable. As the name suggests, the real essence has its basis in reality as opposed to simply in the human conception. Nominal essence, by contrast, is comprised of the abstract, observable qualities of a substance, those which enable us to classify substances into different species or genera. Locke uses the term ‘nominal’ to demonstrate that noting the similar abstract ideas in a substance is an exercise in naming things. Locke offers many examples of how the real and nominal essences interact; his most common example is that of Gold. The nominal essence of gold is the idea that we have of gold which allows us to call it gold; certain substances will have certain qualities which match the nominal essence of the thing we called gold e.g. weight, malleability, yellowness etc. and we would call this substance gold also. Meanwhile, the real essence of the gold is allowing it to have the properties which constitute its nominal essence.
It has been noted that in postulating his theory of essences, Locke reacted against his scholastic predecessors, and even their predecessors, specifically Aristotle. He believed their investigations futile; as Mackie puts it, they had an approach to essences which ‘was not merely erroneous but seriously misleading, which had for centuries led thinkers to pursue wrong and fruitless methods of investigation and had made them ‘pretenders to a knowledge they had not.'(J. Mackie Problems From Locke ch.3) He strongly refutes the notion that in their classification of objects into categories, his predecessors actually had some knowledge of the reality of them i.e. of what he would call their real essence, ‘the true essential nature of things.’ (ibid.) Locke is adamant that what we perceive in objects is merely an abstract idea of what they really are; we categorize them according to these characteristics; the scholastic method, in Locke’s view, gives rise to the dual misconception that we can have knowledge of the fundamental nature of things and that nature organizes substances into separate species itself. Though nature provides the fundamental constitutions of substances which enable them to have the powers to produce certain perceptions in us, it is humans that organize them according to these perceptions.
It sometimes seems that Locke is arguing that the existence of natural kinds is an empirical question and he wants to assert that our knowledge of the nominal essences of substances isn’t enough to infer that there actually are natural kinds.( J. Mackie Problems From Locke ch.3) However, it does also seem that Locke argues towards the denial of natural species on numerous occasions. For example, he claims that if nature were responsible for the separation of substances into species, we couldn’t account for the number of cases whereby substances don’t seem to fit into any species; he states that the view ‘which supposes these Essences, as a certain number of Forms or Molds, wherein all natural Things, that exist, are cast, and do equally partake, has, I imagine, very much perplexed the Knowledge of natural Things. The frequent Productions of Monsters…Changelings, and other strange Issues of humane Birth, carry with them difficulties, not possible to consist with this Hypothesis: Since it is as impossible, that two Things, partaking exactly of the same real Essence, should have different Properties, as that two Figures partaking in the same real Essence of a Circle, should have different Properties.’ (Locke, An Essay Concerning Human Understanding, III, III,17) In addition, he argues that the fact that humans have to be selective in deciding the necessary and sufficient conditions for a substance to fall into a specific species is testament to nature’s lack of categorization. Often, substances have too many similarities, humans must sift through them to decide the most important; this selection process is not something which nature can do. Ayers summarizes Locke’s stance regarding real and nominal essences succinctly: ‘…the Lockean nominal essence is intrinsically an epistemological essence and nothing more, a criterion by reference to which we mark off the members of the species. The boundary marked is a precise one which owes its existence to our drawing it: reality itself simply could not, in Locke’s view, supply such a boundary. Reality can supply resemblances, but resemblances do not constitute natural boundaries.’ (Ayers,’Locke versus Aristotle on Natural Kinds’, Journal of Philosophy 1981)
In conclusion, the individual notions of substance, real essence and nominal essence are inextricably linked within Locke’s epistemological theory; though there are certain points within the Essay Concerning Human Understanding at which one might pause to question how we interpret Locke, overall, the way in which the three elements relate to one another is clear. Locke certainly made a considerable leap in the direction of empiricism and, as Ayers observes, ‘Locke was neither alone nor the first in the field but his argument is the most extended, elaborate, and sophisticated, and certainly the most widely read and influential of his time on the subject of natural kinds.’ (ibid.)