Maurilio Lovatti


General Ideas and the Knowability of Essence:  Interpretations of Locke’s Theory of Knowledge  

Is Locke a conceptualist or a nominalist? Numerous supporters of these two opposing interpretative hypotheses are to be found amongst scholars, and Locke’s concept of universals is the subject of reconstructions which often differ greatly.

In a situation of this sort, it is easy to yield to the temptation to attribute the origin of the divergence to a purely terminological ambiguity. Perhaps the word “nominalism” is understood in different senses? Apparently not. Almost all writers, explicitly or implicitly, agree in considering nominalism to be a doctrine according to which universals exist only as names which are used to designate collections of concrete individuals. Thus, according to nominalism, there are universal terms (common nouns) and there are neither universal entities which exist in reality (for all existing things are particular), nor abstract, universal ideas existing in the mind. In modern philosophy the positions of Berkeley and Hume are generally considered nominalist.

According to various scholars, Locke’s position is essentially the same as the nominalism of Berkeley. This interpretation is based principally on Locke’s assertions in paragraph 9, chapter xi, Book II, of An Essay Concerning Human Understanding.

Locke writes:

“…the mind makes the particular ideas, received from particular objects, to become general; which is done by considering them as they are in the mind such appearances, separate from all other existences, and the circumstances of real existence, as time, place, or any other concomitant ideas. This is called abstraction, whereby ideas taken from particular beings, become general representatives of all of the same kind; and their names, general names, applicable to whatever exists conformable to such abstract ideas.”1

To prove this thesis, Locke uses the idea of whiteness as an explanatory example: the white observed in milk is considered as a representative of the same colour received from chalk or snow, if it has been separated, by a mental operation, from other simple ideas with which it was before connected.

If one considers this paragraph in isolation from the rest of Book II and, especially, from the content of Book III, the following conclusions may be drawn:

a) Notwithstanding Locke’s numerous references to the possession and awareness of abstract or general ideas on the part of the human mind, these abstract ideas are none other than particular ideas used as representatives of or signs standing for a class of individuals: what is universal is only the name.

b) The abstraction to which Locke refers corresponds to that which the Scholastics called “improper” or distinguishing, which consists in mentally separating a characteristic, a quality or a part of a known thing from all of the others contemporaneously perceived; this kind of abstraction is radically different from that which is “proper” or non-distinguishing and which allows us to experience the (universal) nature or essence in the perception of the particular.

c) Locke’s conception of abstraction would not therefore be incompatible with that of Berkeley; on the contrary, Berkeley’s attribution to Locke of a belief in the existence in the mind of general, abstract ideas in reality distinct from particular ideas would seem a polemical exaggeration.

These considerations would make plausible Locke’s classification as a nominalist (for instance, John Yolton, argues that Locke’s theory about general ideas is in fact quite similar to Berkeley’s own account and he claims that, for Locke, abstract or general ideas are fictions2). In my opinion, these would be incorrect and inadequate interpretations of Locke’s epistemology, based upon an arbitrary isolation of the text cited above from the rest of An Essay Concerning Human Understanding. It should be noted that:

  1. The principal aim of Book II is to demonstrate that all of man’s ideas come from experience and that complex ideas are based upon the simple ideas due to sensation and reflection, which are compared and combined by operations of the mind. From this point of view, the distinction between particular and universal ideas is of marginal importance. In fact, Locke warns at the beginning of Book I that he will use the term idea “to express whatever is meant by phantasm, notion, species, or whatever it is, which the mind can be employed about in thinking” (I,i,8), and hence includes in the semantic category “idea” both individual mental representations (images and phantasms) and universals (notions and species).

  2. As Locke explicitly states, the examples given in chapter xi of Book II (which deals with mental operations), “the instances, I have hitherto given, have been chiefly in simple ideas”; chosen, that is, for the purpose of clarity and to further the aim of Book II, with the explicit warning that “Of compounding, comparing, abstracting, etc. I have but just spoken, having occasion to treat of them more at large in other places” (II, xi,14).

  3. In Book III, Locke states that

the sorting (…) under names is the workmanship of the understanding, taking occasion from the similitude it observes amongst them, to make abstract general ideas, and set them up in the mind, with names annexed to them, as patterns, or forms, (…) to which, as particular things existing are found to agree, so they come to be of that species, have that denomination, or are put into that classis. (…) And when general names have any connexion with particular beings, these abstract ideas are the medium that unites them: so that the essences of species, as distinguished and denominated by us, neither are, nor can be any thing but those precise abstract ideas we have in our minds”(III, iii, 13).

This text is not ambiguous: although for Locke abstract ideas are the connection between general terms and particular things (which are known by means of ideas), it is clear that the link (medium) cannot be identified with either of the two elements which it connects: an abstract idea cannot be a particular used as though it were a universal. In other words, that which determines the universality of an abstract idea for Locke is not simply its relation with a number of particular ideas, as for Berkley, but something inherent in and characteristic of the idea itself, the nominal essence which distinguishes all complex ideas (all kinds of complex ideas: of modes, relations and substances).

As far as simple ideas are concerned, Locke thinks that the names of simple ideas, and those only, are incapable of being defined, because what distinguishes simple ideas is that they are not analysable into component ideas. This Locke’s thesis is not inconsistent with a careful distinction between simple abstract idea and simple particular idea, between the concept of green and the percept of green as individual mental representation (this green I see) or the image of green. Therefore which determines the universality of an abstract idea is something characteristic of idea itself as well for simple ideas.

In both these kinds of general idea (of complex and simple idea), the idea is universal in its own nature, i.e. it is made general by abstraction and it, unlike the particular ideas from which it was abstracted, is capable of serving as a standard by which to rank real existences. This might seem a violation of the fundamental principle of Locke’s nominalistic metaphysics, the principle that all existing things are particular. But, as Vere Chappell says, it is not really so:

For this principle applies only to the realm of real existence. This includes physical objects, and their qualities, which are outside people’s minds; and it includes the actions and events that occur within minds, includes acts of perception and thought. But it does not include the intentional objects of such acts, which is what ideas are according to Locke…” 3

I do not think that there are evident contradictions between the examples of abstraction given in Book II and the broad theory of language presented in Book III. There is simply a difference of approach and aims and thus, in the final analysis, a complementarity.

This claim is consistent with R.I.Aaron’s view about Locke’s abstract ideas theory. Aaron gives the following account of Locke’s theory: the general character of Locke’s theory of universals “is not a fully integrated theory ,yet it points steadily in one direction, namely, conceptualism. Realism is rejected; the universal is never one entity amongst others in the world of existences, nor is it a real essence… Locke’s theory excludes nominalism as well as realism”4.

Aaron finds three doctrines of abstraction in Locke’s Essay 5:

  1. an abstract idea is a particular idea which “represents” many other particulars; it was Locke’s first crude thought (and the Berkeley of The Principles reverted to a point of view long since abandoned by Locke);

  2. an abstract idea is what remains when, from a number of particular ideas, all features except those which are common have been dropped from attention (this doctrine is predominant in Book II);

  3. an abstract idea is the essence meant when the general term is used; this doctrine is capable of including within itself the second doctrine and it is predominant in Book III. Considering the progressive development evident in Locke’s thought throughout the Essay, his later position represents his more mature thought.

Greatly widespread amongst scholars is the legend according to which Locke shows a strong aversion to abstract ideas, similar to that of Berkley in the Treatise. This legend is endorsed by influential commentators on Locke. A. C. Fraser writes:

Locke has everywhere a sober dread of abstractions, and clings to the particular and concrete, with a sense of the risk of losing the real in the emptiness of the universal”6.

In reality this supposed aversion does not exist; on the contrary, Locke does not even propose the reduction of ideas to “mental images” (a reduction which in Berkeley and Hume will form the base of the negation of the existence of abstract ideas in the mind).

Locke is not in the least afraid of abstract ideas; his constant concern, which is evident in his treatment of the complex question of the relation between real and nominal essence, is to refute the view of the Scholastics, according to which a universal concept in the mind (post rem) reflects the universal present in all things as substantial form (the universal in re), without assuming positions which are purely conventionalist and nominalist with regard to knowledge, such as those of Mer­senne, Gassendi, Hobbes and sceptical and anti-Cartesian free-thinkers.

According to the view of the Scholastic in seventeenth century, as in the Aristotelian hylemorphic account of material things, all the individuals in the same sort are determined by an identical form ( differences among individuals are determined by the “materia signata”) and the real essence of every individuals of the sort is immutable, because it is created by God. R.L. Amstrong writes:

for a traditional metaphysician like Sergeant, the relation between external objects and the knowledge of them in the mind is identity; the notion in the mind is the very thing itself, its form.”7

On the contrary, according to Locke, “take but away the abstract ideas by which we sort individuals and rank them under common names, and then the thought of anything essential to any instantly vanishes” (III, vi, 4). According to Locke, there are no essential properties, no identical substantial form in all the individuals in the same kind or specie and therefore abstract ideas are made by the mind and not by nature: “particular beings, considered barely in themselves, will be found to have all their qualities equally essential; and everything in each individual will be essential to it or, which is more, nothing at all.” (III; vi, 5) And again:

general and universal belong not to real existence of things; but are the invention and creatures of the understanding, made by it for its own use, and concern only signs, whether words, or ideas (…) universality belongs not to things themselves, which are all of them particular in their existence, even those words, and ideas, which in their signification, are general” (III, iii, 11).

To show why Locke’s view of knowledge is not a conventionalist one, I must offer an analysis of the relation Locke makes between real and nominal essence, with regard to the relations which link term to idea and idea to things. For Locke, the term is the sign (mark) of an abstract idea and the idea itself is the sign of a plurality of things.

The relation between the name and the idea is, in the final analysis, arbitrary:

“…words, which were by nature so well adapted to that purpose, came to be made use of by men, as the signs of their ideas; not by any natural connexion, that there is between particular articulate sounds and certain ideas (…); but by a voluntary imposition, whereby such a word is made arbitrarily the mark of such an idea. The use then of words, is to be sensible marks of ideas…”(III, ii, 1).

The nature of the relation between signifier and signified is variable, though, in the relation between ideas and things with respect to the various kinds of complex ideas which the human mind may frame. The greatest difference is to be found between complex ideas of mixed mode and complex ideas of substance. With regard to the essences “of the species of mixed mode”, Locke points out that they “are not only made by the mind, but made very arbitrarily, made without patterns, or reference to any real existence.” (III, v, 3).

With regard to ideas of substance in particular, Locke’s thought is interpreted in different and often contradictory ways. Although complex ideas of substance may be reduced to a collection of simple ideas, Locke does not doubt the existence of “the real internal, but generally in substances unknown constitution of things, whereon their discoverable qualities depend” (III,iii,15). The reference of the idea (universal) to things is uniquely determined by the nominal, not the real, essence:

our faculties carry us no farther towards the knowledge and distinction of substances, than a collection of those sensible ideas, which we observe in them; which, however made with the greatest diligence and exactness, we are capable of, yet is more remote from the true internal constitution, from which those qualities flow, than, as I said, a countryman’s idea is from the inward contrivance of the famous clock at Strasbourg, whereof he only sees the outward figure and motions” (III, vi, 9).

Locke insists that nominal essences are not arbitrary because the mind, in forming its complex ideas of substances “only follows nature” and does not join together ideas which do not have a natural connection.

For Locke, man uses a certain discretion in constructing nominal essences, since he chooses perceived qualities considered characteristic of a substance, but this discretion is not arbitrary or unconditional because it is limited to the occurrence of empirically verifiable properties, increasingly so by the growth of the scientific knowledge of nature, although clearly this discretion is never completely eliminated since human knowledge may always be perfected. In Book II, Locke asserts that ideas of substance are all inadequate because they all lack “something we should be glad were in them”, since “desiring to copy things, as they really do exist; and to represent to our selves that constitution, on which all their properties depend, we perceive our ideas attain not that perfection we intend” (II,xxxi,3), but this perfection (the complete identity of real essence and nominal essence) may never be reached. On the other hand, complex ideas of mixed mode and of relations are always adequate (for Locke an idea is adequate if it represents perfectly the archetype on which the mind supposes it is based).

Many scholars attack Locke’s underlying assumption that the nominal essence of complex ideas of substance are not arbitrary. For instance, Robert Anderson acknowledges that according to Locke “man making abstract ideas, and settling them in their minds with names annexed to them, do thereby enable themselves to consider things, and discourse of them, as it were in bundles…” (III, iii, 20) but he holds that “in the light of Locke’s reflections in Book IV, it now appears that nominal essence cannot preserve this utility and this partial conformity to things. For it now seems that there is nothing truly essential to material things, and that they have, indeed, no real essence"8. A similar view is also shared in Italy by Lia Formigari and Rocco Pititto,9 who claim that, according to Locke, the ideas of substances are in the final analysis arbitrary.

Locke’s claims (in chapter vi, Book IV) about unknowability of real essence seem to corroborate Anderson’s view. For instance, about the real essence of gold

we have no idea at all. This being as impossible for us to know, as it is for a blind man to tell in what flower the colour of a pansy is, or not to be found” (IV, vi, 5).

Nevertheless one must underline that the goal of the chapter cited above, in which Locke deals with the truth and certainty of universal propositions, proves that scientific statements about physical objects are not certain. According to Locke only trifling propositions, mathematical and ethical statements are certain. Therefore one can not answer the question about the knowability of real essence basing only on the cited chapter in Book IV: one must consider more entirely Locke’s thought in Book II, III and IV of the Essay.

According to Locke an identical form or essence determining all individuals in the same sort does not exist. There is a real essence of this piece of gold or of that cat, but there is not, in the strict sense, a real essence of gold; hence any universal term has only the nominal essence. Nevertheless it is clear and evident that Locke also uses the locution “real essence” with reference to universal ideas, because he deals with the relation between real essence and nominal one. The reference of ideas to things is not as easy a matter as determining the biunivocal relationship between the constituent elements of a complex idea and the corresponding simple ideas themselves, because the relationship of concomitance of simple ideas and the persistence of this concomitance must be considered. In this sense one can speak of real essence of abstract ideas of substances, as the limit and the ultimate goal to which human knowledge of reality is tending.

One may ask a fundamental question: this unknowability of real essence of a substance which has been asserted by Locke on numerous occasions, is it an unknowability in principal (absolute impossibility) or an unknowability in practice, due to the limitations of science at the time?

Although the question cannot be resolved once and for all, I am convinced that from the overall spirit of the Essay there emerges the idea that human knowledge tends to conform to an objective structure of reality; even though Locke is aware that the complete identity between nominal and real essence is impossible in practice with respect to the knowledge of substances, he remains convinced that this identity constitutes the limit and the ultimate goal of the quest for knowledge.

Locke is aware that the science of his time is inadequate:

“…we are so far from being admitted into the secrets of nature, that we scarce so much as ever approach the first entrance towards them.” (IV,vi,11).

The reasons for this are two: the complexity of the relations between a physical object and all other bodies escapes the scientific knowledge (,11) and the human mind can not understand the relations between the alterations of primary qualities and the secondary qualities we received by the five senses (IV,vi,7).

Locke writes:

We cannot discover so much as that size, figure, and texture of their minute and active parts, which is really in them; much less the different motions and impulse made in and upon them by bodies from without, upon which depends, and by which is formed the greatest and most remarkable part of those qualities we observe in them, and of which our complex ideas of them are made up. This consideration alone is enough to put an end to all our hopes having the ideas of their real essence” (IV,vi,12).

But he adds:

our ideas of substance, which consisting of a collection of simple ideas, supposed taken from the works of nature, may yet vary from them, by having more or different ideas united in them, than are to be found united in the things themselves: from whence it comes to pass, that they may, and often do fail of being exactly conformable to things themselves.” (IV,iv,11).

It should be noted that Locke writes: “they may (emphasis added) fail of being exactly conformable”; actually they do fail, but in principal it is possible for them not to fail, i.e. they could be exactly conformable to things themselves. The very instance of the famous clock at Strasbourg, cited by Locke on numerous occasions, fully bears out this view: the inward contrivance (which stands for the real essence in the metaphor) is unknown by the countrymen, who only observe the external visible movements, because they are unacquainted with the laws of mechanics. According to Locke, a knowledge of substances as a sheer and arbitrary collection of simple ideas is surely diffused, but it corresponds to a superficial and pre-scientific kind of knowledge.

Locke’s analysis of the knowledge of substances in Book III and IV anyhow does not make void the criticism to the concept of substance in Book II. According to Locke the substances are not the ultimate constituent of the matter, but they are the link between the continuum of matter and the discontinuous we experienced through the five senses.

According to Locke the very reality is set up by mechanical phenomena, i.e. by the frame of primary qualities of matter which cause all sensitive distinctive features of things: hence the substances are only the discrete results of human operations of “cutting” the continuum of matter; operations made by the human mind to seek and to isolate comparatively permanent forms of mechanical equilibrium, which marks are the secondary qualities.

There is, in effect, in Locke’s thought a break with the Cartesian view of science: mathematics and demonstration are no longer the only privileged model of knowledge; experiment regains the essential role that Descartes denied it. For Locke, who was a great admirer of Newton, mechanical explanation remains the ideal model for a scientific explanation, but it is not always – in practice – possible (Boyle was also convinced of this) and so the knowledge of nature assumes a merely probable status, having been reached by the process of induction, in contrast to mathematics and ethics which are completely deductive. In fact, Boyle’s research and methods had a profound influence on Locke’s conception of science and in particular on the doctrine of the knowledge of substances. These observations on Locke’s philosophy of science underline the enormous, unbridgeable distance between it and that which Berkeley was to formulate in De Motu in 1721 (defined as “instrumentalist” by K. Popper, as opposed to the “essentialism” of Newtonian physics).

In conclusion, in opposition to other widespread opinions, I claim that: 1) Locke’s concept of abstraction is fully compatible with conceptualism and may in no way be considered nominalist; 2) Locke’s complex theory of knowledge cannot be considered a conventionalist view of science.

Furthermore, the profundity of Locke’s concept of substance with regard to the science of his time will clearly emerge, so as to make evident the inadequacy of Hegel’s judgement in conclusion of his comment on the distinction between real and nominal essence in Locke, which finishes with the famous phrase:

This (philosophising) is a very commonplace account of the matter”.10

Oxford, April 4th , 2004

(Tercentenary John Locke Conference, St. Anne’s College, University of Oxford, 2-4 April 2004)


1 All the quoted passages from Locke’s Essay are token from: J. Locke, An Essay concerning Human Understanding (edited with an introduction, critical apparatus and glossary by Peter H. Nidditch), Clarendon, Oxford 1975.

2 J.W.Yolton, A Locke Dictionary, Basil Blackwell, Oxford 1993

3 V. Chappell, Locke’s theory of Ideas in The Cambridge Companion to Locke, (V. Chappell ed.), Cambridge U.P., Cambridge 1994, p. 42.

4 R.I.Aaron, The Theory of Universals, Clarendon Press, Oxford 1952, p. 36

5 R.I.Aaron, John Locke, 2nd ed., Clarendon Press, Oxford 1955

6 J. Locke, An Essay Concerning Human Understanding (A.C.Fraser ed.), Dover, New York 1959, III, viii, 1, n.1, see S.L. Nathanson, “Locke’s Theory of Ideas”, in Journal of the History of Philosophy, XI (1973), p.38.

7 R.L. Amstrong, “John Locke’s “Doctrine of Signs”: a new metaphysics” in Journal of the History of Ideas, XXVI (1965), p. 374; J. Sergeant, The Method to Science, London 1696 e Solid Philosophy Asserted against the Fan­cies of the Ideist, London 1697.

8 R.F.Anderson, “Locke on the Knowledge of Material Things”, in Journal for the History of Philosophy, III (1965), p. 215.

9 L.Formigari, Linguistica ed empirismo inglese nel ‘600, Laterza, Bari 1970, p.196; R.Pititto, John Locke: mondo linguistico ed interpretazione Athena, Napoli 1984, p.64.

10 G.Hegel, Lectures on the History of Philosophy, translated by E. S. Haldane, Routledge & Kegan Paul, London 1955.



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