It is agreed on all hands, that the Qualities or Modes of things do never really exist each of them apart by itself, and separared from all others, but are mix’d, as it were, and blended together, several in the same Object. But we are told, the Mind being able to consider each Quality singly, or abstracted from those other Qualities with which it is united, does by that means frame to it self abstract Ideas. For example, there is perceived by Sight an Object extended, coloured, and moved: This mix’d or compound Idea the mind resolving into its Simple, constituent Parts, and viewing each by it self, exclusive of the rest, does frame the abstract Ideas of Extension, Colour, and Motion. (Principles, Introduction, §7)
Berkeley and Locke (“all hands”) agree, that is, that qualities are inseparably mixed in their real existence, but when Locke further maintins that these qualities can be abstracted from one another in the idea — that is where an absurdity is supposed to come in. The passage Berkeley is alluding to reads, however, as follows:
Though the Qualities that affect our Senses, are, in the things themselves, so united and blended, that there is no separation, no distance between them; yet ’tis plain, the Ideas they produce in the Mind, enter by the Senses simple and unmixed. For though the Sight and Touch often take in from the same Object, at the fame time, different Ideas; as a Man sees at once Motion and Colour; the Hand feel[s] Softness and Warmth in the same piece of Wax: Yet the simple Ideas thus united in the same Subject, are as perfectly distinct, as those that come in by different senses. (Essay, 2.2.1)
Locke does describe a separation here, but it is not a separation of ideas, nor is it accomplished by any act of the mind. He places the separation in question rather between the thing (res), in which the qualities are united and blended, and the mind, into which the corresponding ideas enter already separated: simple and unmixed. The separation about which he and Berkeley disagree is supposed to occur, in other words, at a point which does not exist at all in Berkeley’s system, namely at the interface between the real and the ideal. Some care will therefore be needed in correctly expressing Berkeley’s objection.
Simple ideas, according to Locke, enter the mind only via an operation of perception, narrowly understood — that is, an operation either of sensation or of reflection. But this (passive) operation always precedes the active operation of abstraction:
The Senses at first let in particular Ideas, and furnish the yet empty Cabinet. . . . Afterward the Mind proceeding farther, abstracts them. (1.2.15)
These simple and unmixed ideas are, on their first entrance into the mind, particular, not abstract. To report the disagreement between Locke and Berkeley in neutral terms, then: it is a disagreement, first of all, about what particular ideas we have, and then only secondarily about the possibilities for what Locke calls “abstraction.” It is agreed on all hands that certain qualities are inseparably united and blended in real existence, but it is not agreed on all hands what “real existence” is: where Berkeley locates the (particular) res, namely in the mind, Locke sees only a particular idea, and there, he says, the separation has already occured — the inseparable blending was only in an external res whose very possibility Berkeley denies. To repeat, then: Locke’s particular ideas already contain the separation that Berkeley considers absurd.
The disagreement, moreover, does not reach every case of that supposed separation. Consider, for example, some particular apple. According to Locke, its secondary qualities — for example, its color and its smell — are all inseparably blended in the apple itself. This must be so, since secondary qualities, according to him, are bare powers: are not, that is, really distinct from the subject in which they inhere, and hence not really distinct from one another.[1]See 2.8.24, and see also Boyle, The Origine of Formes and Qualities, p. 19: “They are not in the Bodies that are Endow’d with them any Real or Distinct Entities, or differing from the Matter its self, furnish’d with such a Determinate Bigness, Shape, or other Mechanical Modifications.” And, on the other hand, Locke of course considers that these ideas of color and smell enter the mind simple and unmixed. But there is no disagreement with Berkeley. A thing (res) such as an apple is, according to Berkeley, a collection of distinct ideas:
Thus, for Example, a certain Colour, Taste, Smell, Figure and Consistence having been observed to go together, are accounted one distinct Thing, signified by the Name Apple. (Principles, Part I, §1)
The color and taste of a particular apple are, then, according to Berkeley, realiter distinct — distinct in the thing — and, therefore, consistent with his principles, he holds that each can be conceived separately from the other.
I may indeed divide in my Thoughts or conceive apart from each other those Things which, perhaps, I never perceived by Sense so divided. Thus I … conceive the Smell of a Rose without thinking on the Rose itself. So far I will not deny I can abstract, if that may properly be called Abstraction, which extends only to the conceiving separately such Objects, as it is possible may really exist or be actually perceived asunder. (Part I, §5)
What Locke affirms and Berkeley denies, in this case, is that there is somewhere (outside the mind) a real nexus between the color and smell: the regularity on which the compound reality of apples depends is, according to Berkeley, nothing more than a matter of arbitrary divine syntax.[2]Hence as far as things like apples are concerned, Berkeley’s answer to skepticism is the same as Descartes’s: God is not a deceiver — with the important difference that Descartes thinks this a speculative truth inolving the idea of the infinite, whereas for Berkeley it amounts to nothing more than an expression of my will (to leave by the door and not by the window).
In which cases, then, does Locke actually allow a separation that Berkeley does not? I count at least three, though I am not at all sure the list is exhaustive.[3]There are also some disagreements about the possibility of abstraction that do not depend in any obvious way on disagreements about separability of ideas. The abstract idea of color, for example, that is “neither White, nor Black, nor any particular Colour” (Principles, Introduction, §9), cannot possibly be explained by separating anything within these simple ideas. According to Locke’s actual explanation (Essay, 3.4.16), he would take “there is no human but has some color” to mean, roughly: “all humans have some quality perceptible only by vision.” To determine the true content of Berkeley’s complaint in this case would require a detour into many complications (for one thing, he and Locke do not agree about what “peception by vision” means).
First is the very case Locke mentions in the passage quoted above: ideas belonging to the same sense modality. The example Berkeley mentions most often concerns what might be called the visible primary qualities (visible extension, visible figure, etc.), which he thinks cannot occur without color. Throughout the Principles, indeed, and oddly enough, Berkeley seems to conceive of bodies primarily as visible things. It is difficult to say what Locke thinks about this case, however.[4]Locke says explicitly that the ideas of the primary qualities (except that of solidity!) can enter the mind either by way of sight or by way of touch (Essay, 2.5; 2.13.2). But his response to Molyneux’s question (2.9.8) shows that he doesn’t strictly consider the tangible and visible ideas to be the same. Moreover, since towers which look round from far off may appear square from close by (Med. 6.7, AT 7:76,23–4), visible figure should, by Locke’s own arguments, be accounted a secondary quality (as Berkeley points out: Principles Part I, §14; see also Dialogues III, p. 306, and note once again that Berkeley’s true response to skepticism is the same as Descartes’s). Finally, whatever the status of visible figure and extension, color, at least, is definitely a secondary quality according to Locke, and this implies that we can see no necessary connection between ideas of color and any other idea, or, in other words, that visible figure could in principle appear with no color at all. In one place (Essay, 2.23.11), Locke even appears to claim that this is all microscopic eyes would see. If that actually is his opinion, then the disagreement in this case concerns what is separable in (what Berkeley calls) real existence, not what is separable in the (mere) idea. The case of the tangible primary qualities, including solidity, is clearer. According to Locke, all our knowledge about geometry and rational physics is thanks to the manifest necessary connections between separate abstract ideas of these qualities: these ideas are separately conceivable, but we know that they cannot occur separately (or in the wrong proportions, etc.) in real existence. If the ideas are necessarily connected, moreover, then the corresponding qualities, i.e. powers, in bodies are also necessarily connected, and this establishes a resemblance (isomorphism) between our ideas and things. Berkeley denies that an inert thing can directly necessitate another: denies, that is, that mere affections as such (modes of pure receptivity) can ever resemble an active being. Hence he classifies some of this supposed knowledge as syntactically general representations of empirical regularities — that is, as an attempt to conform our will (qua productive of imagined signs) to the divine will (qua productive of the ideas of sense) — and the rest as trifling: that all figure is extended, for example, is for Berkeley not a connection between separate ideas at all, since every figured idea is also extended.
Second, ideas of pleasure and pain. Locke’s position is the very one that Philonous quickly gets Hylas to give up, namely that, for example, “Pain is something distinct from Heat, and the Consequence or Effect of it” (Dialogues I, p. 187), and similarly for pleasure. Once again, the disagreement is about the separability of, for example, moderate warmth and the pleasure consequent to it in a particular case, and only secondarily about the ability “to frame an abstract Idea of Happiness, prescinded from all particular Pleasure” (Principles Part I, §100). If the disagreement over primary qualities affects the basis of geometry and physics, then this disagreement affects the basis of what Locke projects as an even more important demonstrative science, namely ethics. In this case, Locke does not claim any theoretically manifest necessary connection between ideas,[5]Locke’s ethics is supposed to be demonstrative, but there is not any direct demonstration, as in Hobbes or Spinoza, of the connection between pain or pleasure and any other idea; rather, the connection is supposed to be established — in the Essay, at least — by way of the existence and nature of God. (The imperfection in myself which starts off Locke’s cosmological proof is not, as in the Third Meditation, doubt, i.e. a species of uneasiness, but rather, implicitly, the possessing a beginning in time: see 4.10.2–3.) but we do find, so to speak, a practically necessary connection: the desire of pleasure and the aversion to pain are “Innate Practical Principles, which (as practical Principles ought) do continue constantly to operate and influence all our Actions, without ceasing” (Essay, 1.3.3). Berkeley must deny that there are such general principles. Whether this can be connected to the larger ethcial and political disagreements between him and Locke, I do not know.
Third, and of most interest from a metaphysical point of view, are the transcendental ideas of existence and of unity, which “are suggested to the Understanding, by every Object without, and every Idea within” (2.7.7).[6]The idea of power (2.7.8) is in some respects similar to these, except that power is always only real (associated with the mediate object), not ideal (associated with the immediate object, i.e. the idea, itself). If to these three we add also the simple idea of limit, we obtain a list of four transcendental ideas corresponding to the categories of quantity (unity), quality (limit), relation (power), and modality (existence), or in Locke’s terms to the four sorts of agreement and disagreement of ideas (identity–difference, relation, necessary coexistence, real existence). According to Berkeley, there is no idea of power: I represent power by having power myself, not by having an idea of it. He also presumably would deny that there is a separable idea of limit, though I’m not aware of any place where he discusses that directly. Berkeley rejects the idea of unity as part of his critique of abstract arithmetic (Principles, Part I, §13), and, as for the idea of existence, he sees it as implicated in Locke’s absurd realism: “For can there be a nicer Strain of Abstraction than to distinguish the Existence of sensible Objects from their being perceived, so as to conceive them Existing unperceived?” (Part I, §5).
If Locke genuinely disagrees with Berkeley about this, he must hold that when I know or judge some thing, \(a\), to exist, my act involves two distinct ideas: the idea of \(a\), on the one hand, and the idea of existence, on the other. That in itself is strange enough. It becomes stranger still if we consider more closely the passage from 2.7.7 quoted above, along with what immediately follows there:
When Ideas are in our Minds, we consider them as being actually there, as well as we consider things to be actually without us; which is, that they Exist, or have Existence: And whatever we can consider as one thing, whether a real Being, or Idea, suggests to the Understanding, the Idea of Unity. (2.7.7)
If the same idea of existence, call it \(E\), covers both the ideal case (the existence of an idea) and the real (the existence of a thing, or in other words of a subject of powers and operations: a substance), then knowledge of existence, whether ideal or real, consists in the perceiving an agreement between that idea, \(E\), and some other idea.[7]Berkeley, for his part, denies that either “existence” or “knowledge” applies univocally to cases of ideas and of substances (spirits): see Principles, Part I, §142. Hence, to take Locke’s example: the demonstration of God’s existence, based in part on the intuitive premise that I myself, at least, exist (see Essay, 4.10.2 and 4.3.21), establishes an agreement between the idea of God and \(E\), mediated in part by the agreement between \(E\) and my idea of myself. Or, in general: if \(A\) is my idea of some thing, \(a\), then I know that \(a\) exists by perceiving an agreement between \(A\) and \(E\).[8]Note, incidentally, that there is no thing \(e\) that is the cause of my perceiving \(E\). Hence although \(E\) is not innate, it is what Kant would call a priori. The same holds for the other transcendental ideas listed above. What is strange, however, is that my knowledge that the idea itself, \(A\), exists, must also consist in a perceived agreement between \(A\) and \(E\). How can it be both?
Locke, unfortunately, says practically nothing about ideal existence. He does say quite a bit about real existence, though. Knowledge of real existence — perception of “actual real Existence agreeing to any Idea” (4.1.7) — is the fourth and last sort of knowledge on Locke’s list, corresponding to Kant’s category of modality. Now, this formulation may suggest a tempting way of evading the question posed above: why not think that the idea of “actual real existence” is simply a different idea, according to Locke, than the idea of ideal existence? Then to know that \(A\) exists would be to perceive agreement between \(A\) and one idea, call it \(E_{\text {ideal}}\), whereas to know that \(a\) exists would be to perceive agreement between \(A\) and some completely different idea, \(E_{\text {real}}\). But, besides that our passage at 2.7.7 speaks strongly against this solution, it would also lead to various undesirable consequences. Perhaps most importantly, it would mean that Locke is not strictly speaking a realist, that is, someone who believes that both ideas and things exist, since there would be no sense of “exist” that applies correctly to both.[9]This problem is serious for Locke and not for Berkeley because of their differences over the proper function of language. For Berkeley, “Both ideas and spirits exist” is a sentence meant to affect the will of the listener directly, rather than by means of any ideas that it may excite in the listener’s mind. For Locke, such a use of language would be illegitimate. So I will proceed on the assumption that there is only one idea of existence, \(E\), and ask: what sort of agreement can it be, between \(A\) and \(E\), such that the perception of that agreement constitutes the knowledge that the corresponding thing, \(a\), exists?
The simple and correct answer is, that it is the fourth sort: the sort of agreement, that is, that we perceive in knowing real existence, and not in any other case. This means, for one thing, that it is not agreement of the first sort, agreement by identity: to know that I exist is not to know that the idea of existence is identical to some component of my idea of myself; or, in other words, the proposition that I exist is not, in Kantian terminology, analytic (or as Locke would say: not “trifling”). But neither is it synthetic in the manner of “The interior angles of a triangle equal two right angles” (second sort of agreement) or “Every solid thing is divisible” (third sort). All of this is as it should be: we don’t want “I exist” to mean that I exist by definition, or that my degree of perfection is such that I exist, or that my qualities are necessarily connected to existence. In a word: all three of the other sorts of agreement give rise to knowledge of what is necessarily the case, whereas what I know here — what I know, in knowing that I exist — is something contingent. The fourth sort of agreement and disagreement between ideas is a contingent sort of agreement or disagreement.[10]If it be objected that, in that case, Locke’s demonstration shows God to exist only contingently: I think that must be conceded. The same is true of the Third Meditation proofs, moreover. A cosmological proof can directly establish necessary existence only if it begins with an imperfect being (world) whose imperfection is characterized as contingency.
It may seem, however, that this answer raises more problems than it solves. For can there truly be contingent agreement between ideas at all? And, even if there can, could there be contingent agreement between any idea and the idea of being or existence in particular? Doesn’t every idea, on the contrary, always represent its object as a being, that is, as existent?
Both of these objections, I think, overlook the same thing about the knowledge of real existence. Consider that Locke allows one other case, besides those of God and of myself, in which we have such knowledge — a case which he describes as neither intuitive nor demonstrative, but rather “sensible.” This third case is very narrow:
The Knowledge of the Existence of any other thing we can have only by Sensation: For there being no necessary Connexion of real Existence, with any Idea a Man hath in his Memory, nor of any other Existence but that of GOD, with the Existence of any particular Man; no particular Man can know the Existence of any other Being, but only when by actual operating upon him, it makes itself perceived by him. (4.11.1)
It would be wrong to conclude, however, from this passage, that such knowledge is so narrow that it concerns only present existence, or in other words that the past existence of the world is not certain, according to Locke, but at best only highly probable:
As when our Senses are actually employ’d about any Object, we do know that it does exist; so by our Memory we may be assured, that heretofore Things, that affected our Senses, have existed. And thus we have Knowledge of the past Existence of several Things, whereof our Senses having informed us, our Memories still retain the Ideas. (4.11.11)
What is true, rather, is that sensible knowledge always involves attributing real existence to the object at some determinate time: either, in sensation, at the present, or, in memory, in the past. Or, we might add, in expectation, in the future. For our possession of demonstrative science means that, in certain special cases, we can deduce the course of the future from our knowledge of the past and present.
This temporal determinacy therefore characterizes sensible knowledge: and not sensible knowledge alone, but, I think it clear, the fourth sort of agreement and disagreement in general. While every idea represents its object as possible, “actual real existence” — note that the expression is by no means redundant — is existence at a determinate time, and, at least in the case of an external object, in a determinate place. This is why, according to Locke, even though many, indeed most, of our ideas are abstract and general, the actual thing corresponding to any idea is always individual, and also why actual existence, in implying individuality, consequently implies spatiotemporal position:
From what has been said, ’tis easy to discover what is so much enquired after, the principium Individuationis, and that ’tis plain is Existence it self, which determines a Being of any sort to a particular time and place incommunicable to two Beings of the same kind. (2.27.3)
Thus both of the above objections are answered. There is always and necessarily agreement (I suppose it is of the second sort?) between every idea and the idea of existence, as attributed to the real object (I am not yet here talking about the ideal existence of the idea itself). But this agreement only means that the idea represents the real object as possible, that is, as existent at some indeterminate time and place. The actual existence of the real object requires a determination to time and place, and the latter determination is always contingent: there is no deriving, from an idea alone, the time and place, if any, at which the corresponding real object exists.
If any: we do have ideas of merely possible things. But Locke puts stringent limits on the cases and the senses in which that is so. A simple idea, for one thing, must always be the idea of something that at one time existed: if it is not a present sensation, it must be a memory. That is the whole content of Locke’s empiricism. The mind cannot make a new simple idea. It follows that, even if (as is usual) we cannot recall that particular time at which we first had some sort of sensation, we nevertheless never have a simple idea without the consciousness that it has been in our mind as a sensation at some determinate time in the past, and “to Remember, is to perceive any thing with Memory, or with a Consciousness, that it was known or perceived before: … This Consciousness of its having been in the Mind before, being that, which distinguishes Remembring from all other ways of Thinking” (1.4.20/21). With regard to their ultimate components, then, our ideas never refer to anything merely possible, but always to something that either exists now or has once existed. A complex idea of substance, moreover, since its corresponding real object is supposed to contain the unknown nexus on which the unity of its component ideas depends, is not adequate to our purposes unless that combination has actually occurred in the past:
No body joins the Voice of a Sheep, with the Shape of a Horse; nor the Colour of Lead, with the Weight and Fixedness of Gold, to be the complex Ideas of any real Substances; unless he has a mind to fill his Head with Chimera’s, and his Discourse with unintelligble Words. . . . For tho’ Men may make what complex Ideas they please, and give what Names to them they will; yet if they will be understood, when they speak of Things really existing, they must, in some degree, conform their Ideas to the Things they would speak of. (3.6.28; see also 2.30.5)
This is why, when meeting a skeptical doubt about the existence of external things, Locke thinks it sufficient to point out that we can distinguish, not between sensation and dreaming, but between sensation and memory:
For I ask any one, Whether he be not invincibly conscious to himself of a different Perception, when he looks on the Sun by Day, and thinks on it by Night; when he actually tastes Wormwood, or smells Rose, or only thinks on that Savour, or Odour? We as plainly find the difference there is between any Idea revived in our Minds by our own Memory, and actually coming into our Minds by our Senses, as we do between any two distinct Ideas. (4.2.14)
In the cases of modes and relations only do we have good (theoretical or practical) reasons to form complex ideas in which the combination depends on nothing but our will and is not intended to refer to anything actual, whether past or present. But, although Locke never says this explicitly, he appears to think that we can usefully form those ideas only within the bounds of the demonstrative sciences (mathematics, physics, and ethics), where a priori connections supply the place of past experience in limiting the range of possibility.
Now, abstraction, according to Locke, consists not in any arbitrary separation of one idea from another, but rather in separation of any idea from its contingent, temporally determinate agreement with real existence, which is the principle of individuation:
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, wherby Ideas taken from particular Beings, become general Representatives of the same kind. (2.11.9)
The ideas that we have prior to this operation, including therefore all the ideas of infants (and of adult non-human animals) are particular:
The Senses at first let in particular Ideas, and furnish the yet empty Cabinet: And the Mind by degrees growing familiar with some of them, they are lodged in the Memory, and Names got to them. Aftewards the Mind proceeding farther, abstracts them, and be degrees learns the use of general Names. (1.2.15)
But these initial, purely particular ideas, are nevertheless simple: that is, as separated from other ideas as they could be. What a child knows before it gets the use of words is, for example, “the difference between the Ideas of Sweet and Bitter (i.e. That Sweet is not Bitter)” (1.2.15), and non-human animals never compound ideas very much, if at all (2.11.7). So what the beast or the infant has is, for example, the sensation of something sweet — that is, of some particular subject of the power to cause it to perceive sweet — here and now; either that, or the memory that such a thing was previously present, which sensation or memory is certainly correct:;
Because being nothing but the Effects of certain Powers in Things, fitted and ordained by GOD, to produce such Sensations in us, they cannot but be correspondent and adequate to those Powers: And we are sure they agree to the Reality of Things. For if Sugar produce in us the Ideas which we call Whiteness, and Sweetness, we are sure there is a Power in Sugar to produce those Ideas in our Minds, or else they could not have been produced by it. (2.31.2)
And, conversely, even if we put into a complex idea enough simple ones that only a single invidual is known to possess all the corresponding qualities (for example, in our idea of the sun: see 3.6.1), as soon as we consider that idea without its contingent, temporally determinate agreement with existence, it becomes fully as abstract as any other. Indeed, this would remain true even if, per impossibile, we could put into our complex particular idea the ideas of every quality belonging to some particular thing (see 2.31.8). In that case, all of those qualities would be known to be necessarily combined in the object of the idea (by the first sort of agreement), but the uniqueness of the object, or in other words the particularity of the idea, would be due neither to any of them severally nor to all of them collectively, but rather to the contingent existence of the object at some determinate time and place (that is, by the fourth sort of agreement). Take that away, and you have always an abstract general idea, to which many distinct objects might in principle correspond.
So much for real existence. Ideal existence is harder to understand. I know some, perhaps most, readers of Locke tend to think of ideas as the objects of reflection, which would at least promise to make real and ideal existence parallel cases. But to me that seems a fundamental mistake. The immediate object of a mental operation — whether of sensation, of reflection, or of any other — is always an idea, but the mediate (real) object never is. The mediate object is always something that is acting, or has acted, or might possibly act on me so as to cause me to perceive the immediate one. Thus the mediate object strictly speaking is a substance: either a body or a spirit. However, we can also think of the mediate object as the quality, that is, power, faculty, of that substance, by virtue of which it can so affect me. Or we can think of the object as the actual or potential operation of that quality. So if I see something white, for example, we can think of the object as the white substance (e.g., a snowball), or as the quality of whiteness in that substance (the whiteness of the snowball), or as the operation of that quality (its looking-white-to-me-now, so to speak). And similarly, when I reflect on myself qua sensing something, we can think of the object as the sensing substance (my mind), or as the quality of sensitivity in that substance (the faculty of sensation), or as the operation of that quality (this individual mental operation of sensation). In practice, Locke tends to mix the different ways of speaking: “our Observation [is] employ’d either about External sensible Objects; or about the Internal Operations of our Minds” (2.1.2). But, whatever reasons he may have for this,[11]It is perhaps connected to the fact that the mind has no primary qualities, since all its faculties are nominal, not real: see 2.21.6. I will return to this point below. it remains clear that no idea is mediate object, either in sensation or in reflection. On the contrary, when I reflect on sensation, the only idea that is my object at all is the immediate object, namely, the simple idea of sensation itself.
If an idea is only ever immediate object of perception, then there is no room for distinction between the time at which it is known to exist and the time at which it exists. If I now perceive some sort of agreement between an idea, \(A\), and the idea of existence, \(E\), and my perception of that agreement is supposed to consitute my knowledge that \(A\) exists, then what I know must be that \(A\) exists now. When I am no longer perceiving this idea (no longer perceiving numerically the same idea), I can no longer perceive its agreement or disagreement with anything. Every idea therefore agrees with the idea of existence always and necessarily in two quite different ways, and the difference is reflected in the different, indeed opposite, temporal character of the attributed existence: every idea represents some real object as existing at some completely indeterminate time, while the idea itself always exists now and at no other time whatsoever. Or perhaps I should say that there is only one agreement, which presents different aspects as we regard it either subjectively or objectively. This agreement — which, again, I guess is of the second sort — does not itself involve any temporal determination. So I perceive it to apply to the idea exactly when I perceive the idea itself, and I perceive it to apply to the mediate object at no determinate time. And this helps explain why Locke feels no need for a separate treatment of ideal existence: knowledge of actual ideal existence is really neither more nor less than knowledge of possible real existence.
This is the best I can do at present to make sense of what Locke says about these matters. I must admit that I am not entirely happy with it. The main question that bothers me: why, if all the above is correct, does Locke say that my sensible knowledge of the actual real existence of bodies is “not altogether so certain” (4.11.3) as my intuitive knowledge of my own actual real existence? My situation is the same in both cases. In case of memory or of sensation, I not only perceive the sort of agreement between the idea of existence and my idea \(A\) which constitutes knowledge of the (present) ideal existence of \(A\), but also another agreement, of the fourth sort, between the idea of existence and \(A\): the sort of agreement the perception of which constitutes knowledge of the (temporally determinate) existence of a substance \(a\) (a substance with the power to cause me to perceive \(A\)). What difference does it make which substance \(a\) happens to be? Why is this perception more certain if \(a\) is the substance that I myself (currently) am?
I suspect that I could answer this question if only I understood better what Locke is even saying. The certainty of sensible knowledge is different from any degree of probability, no matter how high. As I write these words, for example, it happens that no human beings other than myself are present to my senses, although I am not entirely alone: a cat is sleeping on the sofa across the room. Of the existence of other human beings, therefore, I have, according to Locke, only a highly probable judgment (opinion):
And therefore though it be highly probable, that Millions of Men do now exist, yet whilst I am alone writing this, I have not that Certainty of it, which we strictly call Knowledge; though the great Likelihood of it puts me past Doubt, and it be reasonable for me to do several Things upon the Confidence, that there are Men (and Men also of my Acquaintance, with whom I have to do) now in the World; But this is but Probability, not Knowledge. (4.11.9)
Of the cat’s existence, on the other hand, I do have such certainty (I can look at her directly while touch-typing these words). How can my certainty of the cat’s existence be, so to speak, more certain than any probability, and yet still not altogether so certain as the certainty of my own existence?
What occurs to me in this regard is that sensible knowledge has two parts, one of which is certain while the other is not. It is certain that some substance now operates so as to cause in me the perception of some ideas, which ideas belong to (although they do not exhaust) my complex idea of Lily, the cat. But that the substance in question is Lily, or even that it is a cat, can only be, at best, highly probable. And perhaps, according to Locke, it is not even quite certain that the substance in question is a body. Or at least: if that is certain (or would be certain if I were feeling Lily rather than merely seeing her, i.e. if I were perceiving her tangible primary qualities), it is not certain that the substance is different from my mind, since it is not certain, according to Locke, that my mind is not a body. When Locke offers evidence against skepticism, he aims to refute a skeptical doubt of this nature: due to the vast difference between seeing the sun and remembering having seen it, everyone, he says, “hath a certain Knowledge, that they are not both Memory, or Actions of his Mind, and Fancies only within him; but that actual seeing hath a Cause without” (4.11.5).[12]Hume uses this same phrase, “action of the mind,” and in the same sense, in his own discussion of real vs. ideal existence at Treatise 1.3.8.16. It may be hard to notice this because, again, of the difference between what Hume and Locke think “real existence” is. To believe in the existence of an external thing, such as a table, is, according to Hume, to have an idea which is a copy of and draws force and vivacity from a certain impression, which impression we ordinally take to be, not a representation of the table, but rather the table itself. Similarly, to believe in the existence of a mental operation, e.g. an act of memory or imagination, is to have an idea which is a copy of an idea, and also a copy of that idea’s special je-ne-sais-quoi character of mental activity, which we ordinarily take to be, not a representaion of the mental operation, but rather the operation itself. Even though the first idea is a mere copy of the impression (i.e., of the table), its character of mental activity is original to it: in that respect, then, the first idea is an impression, and can be source of force and vivacity for the second. A similar question could not arise about my perception of myself, then, just because acts of reflection, since they do not represent any primary qualities, do not represent any substance at all per se. The mediate object of an act of reflection is represented simply as whatever substance operated to cause that act — to cause the perception of, for example, the idea of sensation:
When we see, hear, smell, taste, feel, meditate, or will any thing, we know that we do so. Thus it is always as to our present Sensations and Perceptions: And by this every one is to himself that which he calls Self ; it not being considered in this Case, whether the same Self be continued in the same, or divers Substances. (2.27.9)
There is no room for error here, not because the act of reflection has superior access to its object, but rather because it claims so little about it.
But although it would make sense for Locke to say this, I am unhappy because I can’t persuade myself that he actually is saying it. The passage I cite above, “he hath a certain Knowledge, that they are not both Memory,” actually seems to tell against it: Locke there explicitly attaches certainty to sensation in the very respect in which I suggested it leaves room for doubt (and this in the case of the sun, whose tangible primary qualities, I suppose, we never perceive[13]Unless someone could be said to perceive the tangible position of the sun by feeling the monthly variation of the tides?). So I remain confused as to what Locke means.
Returning, in any case, to the dispute with Berkeley: we may now observe that Berkeley, in maintaining that there is no separable idea of existence, is really maintaining both his idealism and his whole case against abstraction. In perceiving Locke’s fourth sort of agreement, we perceive that something actually is or was present, but only contingently, at the same time and place as our idea; hence we perceive the presence of something distinct from our idea. On the other hand, when we regard the same idea apart from that agreement, it represents its object as possibly present, at no determinate time and place, and in that way becomes general, in the sense that different substances, at different times and places, can all agree with it, just so long as they all have the power (quality) to cause perception of such an idea. Berkeley’s idea can never become general in Locke’s sense because it was never particular, in that sense, to begin with: we do not perceive in it any connection to a determinate temporal position. Its position depends only what cannot be perceived, namely, a will, whether human or divine.
