The deprivation of anything whose possession is consistent with the nature of the Being which wants it, is a defect. But ignorance is the deprivation of something which is consistent with the nature of intelligence: it is a deprivation of knowledge. Therefore ignorance is an intellectual defect, imperfection, privation, or shortcoming.
—James Frederick Ferrier
The aim of this chapter is to sketch the contours of the concept of ignorance. The task is not simply a matter of consulting the dictionary and reviewing common usage; because it reveals contested and subtle issues, it requires doing philosophical work and taking positions on these issues. The analysis inevitably entails argument. At this early stage, precision is less important than evocativeness; elaboration and refinement will continue through the book. First, however, we must deal with the quirkiness of the concept.
Despite its ubiquity and importance, whenever we try to think seriously or talk insightfully about ignorance, especially about our own ignorance, we step into a muddle. We encounter two conceptual peculiarities that may lead to frustration, irony, or futility. Together, they suggest that any attempt to understand ignorance is impossible and to pursue the topic is folly.
The first arises from the negativity of the concept; the second concerns the implicit paradox in understanding our ignorance. Neither is as problematic as it first might seem, but the wise course is to confront both at the outset. As you might guess, I will conclude that neither concern should dissuade us.
Privatives, or negative concepts, are those that indicate an absence, deficiency, or loss of something. Our use of them is a tribute to our capacity for abstract thought, and they can be philosophically complex and deceptive. Ignorance is a privative: it is, at its core, a lack of knowledge or understanding (though I will argue it is not merely this). We will need, therefore, to examine an absence, a privation, a deficiency, a negative state or property. Talking about an absence seems to turn it into a presence, in the way that talking about nothing seems to transform it into a something: nothingness. At first glance, this is only linguistic sleight-of-hand, an illusion of syntax that results from treating all nouns equally. That trick, however, can ensnare the unwary in metaphysical tangles.
The traditional concern is a fallacy of reification: the error of taking what is merely a negation to be a real entity. In some contexts, that mistake is blatant to the point of silliness. For example, if I were to say, “I saw no one in the office,” it would be ridiculous to ask whether “no one” was sitting or standing. If I tease a child by saying, “You may eat the donuts, but be sure to leave the holes,” the reification is deliberate and funny, like the playful nonsense of Lewis Carroll. I too would be exploiting the fallacy to perplex or delight.
But this might take a more serious turn: my little joke might lead to musings about just what sort of thing a donut hole is, how this one differs from that one, and what it might mean for a hole to be gone. There are grounds for taking holes to be real, if nonmaterial, entities: we perceive them; we can locate, count, and measure them; we often create and use them; we can distinguish actual from possible holes—and yet they are a kind of negativity, an emptiness. What is ontologically proper, what holes really are, is difficult to discern.1
Moreover, there is a baffling array of such negativities, from those that have a physical locus to those that are quite abstract: we speak of the crack in the sidewalk, the holes in Swiss cheese, the vacuum in the pump, the shortage of family physicians, or a deficiency of vitamin D. Many of these negativities may be interpreted alternately as denoting a missing property or as the absence of a particular state of affairs: incongruence, for example, may be thought of as a negative property (the lack of congruence) or negative state (the absent state of being congruent). Negative concepts even appear to function causally, as when the cause of a diver’s death is determined to be lack of oxygen, or the cause of crop failure is the dearth of rainfall, or the absence of a quorum forces cancelation of a meeting. These ascriptions and the common uses we make of them in reasoning need not be fallacious.
Furthermore, from a phenomenological perspective, we do sometimes experience an absence as a kind of presence, as when a loved one is gone and we are aware of a vacant chair, not merely of an extra chair; or when the sudden loss of a charismatic leader is felt as a gap and leaves followers in disarray. In such cases, what is present to us is not a generic absence, but a quite specific one. To use Jean-Paul Sartre’s example: when he arrived late for his appointment with Pierre at the café, Sartre saw the absence of Pierre, not the absence of Wellington or Valéry.2
What sort of negativity does ignorance have? Basic analytic epistemology would say that “Sascha is ignorant of p” means that the proposition “Sascha knows that p” is false. In other words, ignorance is simply a logical negation. Ignorance occurs when the requisite for genuine knowledge is absent. This quickly directs attention toward the substantive question of what is required for knowledge claims to be true—which has been the dominant direction and debate in epistemology for centuries. (One might wonder: if we do not yet know what knowledge is, how can we presume to know what its lack is?)
This traditional view has both narrow and broad implications: it affirms that ignorance has no conceptual content beyond the negation of propositions about knowledge; yet on this account, even a bowling ball is ignorant, because the proposition “A bowling ball knows that p” is false. The innovative epistemologist Timothy Williamson interprets knowledge as the mental state of knowing. Either the state is present (one knows) or it is not (one doesn’t know). One’s claims to knowledge are true when one possesses the mental state of knowing.3 So, what then is ignorance? For Williamson, ignorance is simply the absence of the state of knowing, and thus, again, sticks and stones and bowling balls are all ignorant, for they do not possess the state of knowing.4
My view is that calling a bowling ball ignorant, metaphorical possibilities aside, is a category mistake; that is, it ascribes to an object of a certain category something that is logically inappropriate for objects of that category. It is similar to calling an idea purple or a stone condescending. It is not merely by linguistic convention that we don’t assert such pointless (though true) claims. More than conventions of language are involved: indeed, I think it is conceptually significant that ignorance implies the capacity to learn. It is thus a category mistake to apply the term to things that do not have such a capacity. Moreover, ignorance, not-knowing, may be manifested as a distinctive mental state, or more accurately, a cluster of related states.5 This means that the concept has discernible content; it is more than a mere absence or negation; its negativity may be substantive. I agree with literary critic Shoshana Felman, who concludes: “Ignorance is thus no longer simply opposed to knowledge: it is itself a radical condition, an integral part of the very structure of knowledge.”6
In short, the negativity possessed by the concept of ignorance is not emptiness. It does not render otiose the attempt to study ignorance. Yes, caution is required regarding the sort of reality we give negative concepts. But it is wrong to think that, if we understand knowledge and identify its necessary and sufficient conditions, we will automatically understand all there is to know about ignorance. Would we expect to understand everything about drought simply by understanding rainfall?
It is true that we bestow an intuitive primacy on positive concepts and affirmations; their correlative negative concepts and denials seem wholly parasitic on them. But not all conceptual polarities are fixed; many may be reversed, as with a figure–ground reversal. We can view silence as the absence of sound, or sound as the absence of silence, depending on context and on our desires and purposes. The same is true of ignorance and knowledge.
The concept of ignorance carries a second, compounding peculiarity. I noted this paradox earlier: How can I know that which I do not know? Must not any attempt to understand ignorance alter it, and any successful attempt, destroy it? Ignorance seems necessarily to defy understanding. It is opaque, a blank label for the unknown; as a signifier, it merely points to what we do not understand. Won’t ignorance vanish before our eyes as we learn about it?
There is, of course, an elementary confusion in play in this paradox: the confusion between understanding the concept of ignorance and understanding that which we do not understand. Coming to understand the former (alas!) does not vanquish the latter. But that clarification does not completely resolve the problem. In trying to understand ignorance, we hope for more than definitional clarity: we hope to understand the shape of what-we-do-not- know, its varieties, something of its qualities, and its impact on our lives.
The question is how much we can learn about what we do not know. We can progress by tactics such as distinguishing the particular from the general, invoking metalevels of discourse, and parsing different types of ignorance—essentially by identifying with greater precision the particular ignorance to which we refer. We can take into account the perspectives of different knowers and the relation of epistemic events in time. All these techniques will be used in the pages that follow, but for the moment, two specifications may be helpful.
First, ignorance refers not only to the state of not-knowing; it also designates that which we do not know. In that respect, ignorance has what philosophers call intentionality: it takes an object. To be ignorant is to be ignorant of something.7 Objects of ignorance, like objects of knowledge, can vary enormously in scope. What one is ignorant of may range from a specific, fine-grained fact to whole fields of knowledge. This means that an individual may be knowledgeable and ignorant simultaneously—but in regard to different matters. Furthermore, ignorance may also be used sweepingly to refer to all that we do not know, as in the statement, “My ignorance is vast.” In such usage, the implied object is comprehensive but unspecified or unspecifiable. Our apparent paradox exploits the ambiguity of these usages. Coming to know X vanquishes only the ignorance of X—and leaves all our other ignorance untouched.8
We can, therefore, gain knowledge about ignorance; we are not limited to clarifying definitions. Just as one can make precise claims about vagueness, so one can make cognitive claims about ignorance without self-contradiction (“Ignorance abounds,” for example). We can, as I hope to show, learn many significant and specific things about our ignorance and the way it functions in relation to our knowledge.
Second, it is important to specify whose ignorance we have in mind, because the possibilities for affirming knowledge and ignorance shift with perspective. The constraints I encounter in trying to delineate my own ignorance are not the same as those I experience when discussing the ignorance of someone else (although clearly my own ignorance will always be in play). When I talk about your ignorance or someone else’s (making second- or third-person ascriptions), I may know thoroughly that which you or they don’t. But when the ignorance I discuss is mine (a first-person ascription), my epistemic constraints are tighter, and what I can affirm is correspondingly limited. Moreover, one may ascribe ignorance to individuals, groups, large-scale populations, or even the whole human race. This progression of enlarging scope introduces interesting notions of individual, shared, collective, and distributed ignorance. And when we sweepingly refer to universal human ignorance, we designate that which no one knows. If I include myself in any of these plural referents (I am necessarily included in “the whole human race”), I again feel the epistemic constraints of the first-person perspective.
Years ago, I heard the venerated Kant scholar, William Henry Werkmeister, deliver a paper with the cleverly punning title, “Der unbekannte Kant,” or, as he translated it, “The Kant Nobody Knows.” As he began, a wag in the audience immediately asked if “nobody” included the speaker. That backed “Werkie” (his affectionate nickname) into either admitting that even he did not know this Kant, or making the more likely, but slightly off-putting claim that this Kant was known to nobody else except Werkie himself. Or perhaps, that this Kant was known to no one present in the audience except him. But before he could make his painful choice, another wit in the audience asked whether “nobody” also included Immanuel Kant himself. Werkie had not even passed the announcement of his title, and surely the next question would be: “And how do you know that nobody knows this Kant?” Instead, he joined the laughter and quickly began to read. The gentle fun of that moment derives from play on the varying epistemic constraints of first-, second-, third-person, and universal ascriptions of ignorance. The interchange also displays the difference between claiming one’s own knowledge or ignorance, and claiming to know that someone else has knowledge or ignorance.9
The point is fundamental: in the same general way in which questions arise from a perspective of ignorance, assertions or claims derive from a perspective of knowledge (or presumed knowledge). Therefore, all ascriptions of ignorance are necessarily made from a perspective of presumed knowledge: it requires knowledge to identify ignorance. All sincere cognitive claims (assertions that are true or false), even those made about ignorance, declare one’s presumption to knowledge and operate with a norm of truth.10 All attempts to understand ignorance will necessarily build from what is (thought to be) known. To assert that “ignorance abounds” is to assert that I know it to be so—or at least that I believe (I know) it to be so. This explains why, at some level, ignorance doesn’t recognize itself: it does not have the cognitive wherewithal. I stress this basic point because, as we shall see (in part 2), it has troublesome implications.
Because we are capable of learning, claims about ignorance are also affected by temporal reference. One may make a wider range of claims about one’s past ignorance based on current knowledge than one may make about one’s current ignorance. “I thought he was trustworthy, but I did not know his treachery” is, sadly, a judgment that can only be made in hindsight.
This trio of specifications—who is ignorant of what and when—serves to structure epistemic space, opening up room for the understanding of ignorance. It also provides axes for the structure of ignorance.
To summarize: what we initially encounter as paradox does not derail a study of ignorance at the start. The study of ignorance is not disqualified by insinuations of conceptual vacuity or logical impossibility. We do have the realistic, tantalizing possibility of studying ignorance purposefully to gain substantive insights about our lack of knowledge. A caveat is that, however far we may journey toward an understanding of ignorance, when we go beyond the context of our knowledge—particularly when we speak of our own current ignorance or of what no one knows—our grasp will necessarily be oblique or indirect. Our most precious insights are, beyond that point, only intimations.
The etymology is straightforward: ignorance is descended ultimately from the Latin ignorantia, which has the same core meaning; it is a compound of ig- (not) and gnarus (knowing or known). Latin, however, gives us two different verbs: ignoro, which means to be unaware of; and ignosco, which means to overlook, refuse to take cognizance of, disregard, or even to forgive. Interestingly, English has not retained those distinct formulations.11 In contemporary usage—and for centuries previous—the English verb, to ignore, has had the latter meaning, not the former. So for example, when I ignore an annoying pet or someone’s bad manners, it does not imply that I am ignorant of them. On the contrary, one might even say that I must, on some level, know that the annoyance or the faults are manifest in order to ignore them. Oddly, however, we have in English no cognate transitive verb meaning to be ignorant of. The English noun and verb have long gone their separate semantic ways.12
I have accepted as an initial account the standard one: ignorance means a lack of knowledge or understanding, though I noted it is not a full or final account.13 Earlier, I remarked that ignorance is neither stupidity nor irrationality, though they are understandably entangled in practice. Neither should ignorance be confused with error. Error is a negatively normative concept; it marks an action or a judgment or ascription as having failed in relation to some cognitive standard (accuracy, validity, truth, etc.) or performance standard (efficiency, effectiveness, elegance, etc.). One “makes” or “commits” an error, whether by omission or commission. Ignorance, by contrast, requires no action.14 There is, nonetheless, a relationship: ignorance is a frequent cause of error—though there are plenty of others, such as overconfidence, carelessness, and interference. Moreover, we are always ignorant of our errors as we make them, assuming they are unintentional. (“Intentional errors” are, in a deeper sense, not really errors at all: they are deceptions.) And, for better or worse, we may well remain ignorant of our mistakes, once we have made them.15
Is ignorance similarly a normative concept? It is conceptually negative, but is it normatively negative as well? Is ignorance essentially bad? Common usage may suggest that it is. It is true that the flat ascription, “Max is ignorant,” has harsh connotations to our ears; the judgment seems derisive and decisive about Max’s capacity or character. Notice, however, that the harshness lessens as the object of the ascription becomes more narrowly particular. Consider this progression: “Max is ignorant”; “Max is ignorant of poetry”; “Max is ignorant of the poetry of Santayana”; and “Max is ignorant of Santayana’s first draft of that poem.” The last is certainly a weaker condemnation than the first—if it is a condemnation at all. Now consider another set of ascriptions: “Fred is ignorant of his wife’s dalliance, of his mother’s last will, of his son’s password, of his daughter’s whereabouts, of his neighbor’s fantasy life, of his sister’s true parentage, of his cousin’s bank account, of his dog’s fate.” Poor Fred? Bad Fred? Well, perhaps, but we would need to hear more of the soap opera to know whether, in each case, we should judge Fred or his ignorance good or bad, and to what degree. These varying resonances hint at hidden presumptions regarding our expectations or even obligations to know certain things, and our sense of when not knowing is blameworthy, excusable, justifiable—or perhaps even preferable.
Ignorance does denote a lack, but it does not presume that lack is a bad thing. If it is a “negative concept,” it is so only in a logical sense, not in a normative sense. That platitude of fecklessness, “Ignorance is bliss,” may have its times and places. “Knowing too much” is a meaningful phrase. Nevertheless, as I acknowledged earlier, our default assumption is that ignorance is normatively negative. Our “epistemic presets” are these: gaining knowledge is a worthy achievement accomplished by vanquishing ignorance; knowledge has intrinsic worth; and ignorance is debilitating.
It would, however, beg important questions to build this default of negative normativity into the very definition of ignorance itself. I do not want to foreclose at the outset the possibility that particular types or instances of ignorance might be useful or epistemically valuable or morally good. Scrutinizing this presumption and sorting out these questions are parts of the task at hand, so we need to preserve a neutral, descriptive sense of the concept. Going forward, I will take the disvalue of not knowing to be a matter of normal contexts and implications, not of definition. We may find value in what we do not know and in the not-knowing of it, but claiming it will require accepting the burden of explanation and justification that falls on anyone who would advocate ignorance, anyone who would claim that it is ever preferable not to know.
Being ignorant of seems to be the opposite of knowing, but philosophers have distinguished three ways knowing: knowing that, knowing how, and knowing by direct acquaintance.16 Knowing that refers to factual knowledge expressible in propositions (“S knows that p”), such as knowing that “today is Saturday,” “the atomic number of beryllium is 4,” or “John Stuart Mill’s godson was Bertrand Russell.” This form of knowing requires the retention and purposeful retrieval of systematically related vocabularies, concepts, propositions, facts, and conventions. It also limits the range of knowledge to facts that can be given propositional form. The opposite, not knowing that, is the conventional case of ignorance. This formulation requires that what one does not know (designated as p) is a specific fact that can be formulated as a proposition. But specification and propositional form are not possible for many kinds of ignorance: for example, one who is ignorant of trigonometry is not merely ignorant of a fact, or even of a set of facts. Propositional knowledge is but one form of knowledge; it is too restrictive to be exclusive.
Knowing how refers to skills, such as knowing how to jump rope or knowing how to play the pipe organ. This form of knowing requires abilities, techniques, and a competence in performance that is typically earned through practice. Is not knowing how a type of ignorance? The question is not easy, because the answer seems intuitively to turn on the sort of skill we have in mind. When an activity has a relatively low cognitive component, we are less likely to say that not knowing it constitutes ignorance. For instance, we are not apt to think of a person who is unable to jump rope or whistle as ignorant of rope-jumping or whistling; she is simply unskilled. Knowing how to play a pipe organ, however, is more complex. It requires difficult subsidiary skills (such as knowing how to move one’s feet deftly to play the pedalboard) as well as esoteric propositional knowledge (such as the meaning of diapason and the difference between the Choir, Swell, Great, and Solo manuals). In such cases, not knowing how does seem to entail ignorance. In short, it appears that we apply the term ignorance to not knowing how when referring to a complex skill in which are entailed significant cognitive, knowing that, elements. In such cases, one is both unskilled and ignorant of certain relevant knowledge. Gaining propositional knowledge alone will not, of course, make one skilled.
I should acknowledge, however, that some philosophers believe that knowing how is fully reducible or translatable into knowing that. If this reduction were successful, it would mean that skills are merely matters of knowing certain facts, which admittedly may be complex and involve sensitivity to context and minute actions. To be preemptive: I do not believe that project can succeed.17 A more plausible suggestion, however, is that jumping rope, whistling, organ-playing, and perhaps any other skill, always involve tacit knowledge, things the competent rope-jumper or whistler or organist must know but cannot verbalize. What exactly is tacit knowledge? One might interpret it as a type of knowing that in which one is unable to formulate the relevant proposition, or perhaps even recognize it. Or, tacit knowledge might be interpreted as the cognitive infrastructure of a knowing how that cannot in principle be reduced to propositional knowledge—such as our know-how in recognizing familiar faces. Under either interpretation (I will say more on tacit knowledge later), not possessing relevant tacit knowledge would constitute a genuine case of ignorance—even for activities seemingly low in cognitive content.
The third form of knowing refers to unmediated experience, as in “knowing the taste of pineapple” or “knowing Mr. Zorian”; such knowledge requires the experience and memory of immediate contact or direct sensation. One may know of Mr. Zorian and one may know a lot of facts about him, but that is not the same as knowing him. Similarly, you may know many facts about pineapples, and you may even have laid eyes and hands on dozens of them, even read about their taste, but if you have never tasted one, you do not (in this sense) “know the taste of pineapple.”18 Would we say you are ignorant of that taste? Our senses provide knowledge by acquaintance, but would we call a blind person ignorant of color? Perhaps, but our reluctance may be more about the harshness of the word and its entangled association with stupidity.
Though it is difficult to generalize about knowledge by acquaintance, the label we apply may depend on the nature and context of the missing experience. The ascription of not knowing by direct acquaintance is sometimes interpreted as not knowing what something is like or as not knowing qualia;19 it shades into never having experienced and thence into being innocent of, which (as we shall see in chapter 4) are states related to but not identical with ignorance.
Understanding is a term we often use when the first and third forms of knowing are combined, coupled with epistemic justification, and placed in a broader, coherent, cognitive context. “Understanding Heidegger’s thought,” for example, involves many elements of knowing that and of knowing by direct acquaintance various texts; but it requires still more. Moreover, I may know Heidegger and many things about him, but still not understand him. To understand something implies the possession of an insight epistemically deeper than merely “having knowledge of” that thing, but it does also entail such knowledge.20 If I am ignorant of X, I don’t understand X; and if I understand X, I am not ignorant of it. But although not understanding might be a matter of ignorance, it also might result from a lack of imagination or empathy, or from a dearth of experience. If I complain that I do not understand how people in some cultures can eat dogs, my problem may not be a lack of knowledge; one cannot be sure that more knowledge would make me understand.
There are other terms for qualities or states for which knowledge is a necessary component. Wisdom, for example, seems to presuppose relevant knowledge; achieving wisdom would be thwarted by ignorance. Expertise requires specialized knowledge and often great skill. Again, there can be no true expert in X who is ignorant in regard to X. Being a cultured person has a similar cognitive dynamic, requiring pertinent knowledge and social skills. The Greeks had a term, amousos (literally, “without the Muses”), which meant “uncultured,” specifically “unmusical,” “graceless,” “boorish,” and “ignorant.” Appreciating music (in the broad Greek sense of the arts and humanities) was thought to be essential in forming a noble soul. It suggests an interesting conception of ignorance as not being cultured, lacking certain knowledge and precious skills and the understanding and character these would bring.21 The concept suggests that ignorance as much as knowledge shapes or reflects one’s character.
All these forms of not knowing and not understanding may be removed or annihilated by learning, though different modes of learning may be necessary. The range of learning is as wide as the range of remediable ignorance. When we learn the meaning of the Italian word falegname, we replace our ignorance with knowledge (or at least the information) that the word means “carpenter.” When Bill learned to jump rope, however, it is dubious that he was remediating his ignorance. Consider also this case: when she moved into a new house, Jenny formed the habit of placing her keys on a hook she found inside the door. She did indeed learn something—a new behavior pattern—but her learning did not replace anything one would normally identify as ignorance. We would not say that Jenny had been ignorant of this convenient habit beforehand. What we normally take to be required for ignorance is a cognitive deficiency, a lack of knowledge or understanding, and this was not Jenny’s previous situation. So, if ignorance is not the lack of a skill or of a particular experience, neither is it the lack of specific behavior patterns or habits—though we may indeed learn all these things.
I have been painting this conceptual picture rapidly and with a broad brush, so let me offer a summary. We distinguish at least three ways of not knowing: being ignorant of, being unskilled in, and being unacquainted with (or not knowing what it is like). Ignorance does not indicate lack of ability, skill, experience, or specific behavior simpliciter; nor is it a matter of error. Rather, ignorance refers centrally to a lack of knowledge (even when knowledge is bound up with skills), which can also result in a lack of understanding. It may be removed, when possible and practical, only by learning, by coming to know or understand.
This does not mean that all ignorance is removable or remediable. There are limits to knowledge, both practical and theoretical. On the practical level, learning may be incidental or intentional; when intentional, the effort required varies from easy and instantaneous to difficult and lifelong, fading into the practically impossible, with significant individual and group differences in the placement of those limits. Beyond that, there are theoretical limits to knowledge as well. In part 4, we will discuss these limits, but for now it is enough to mark the point that ignorance in general or of a specific matter, may not always, even in theory, be eliminable.
Many of our images of ignorance devolve from naturally privileging the sense of sight as the source of knowledge and light as its medium; most are normatively negative. The ignorant are “in the dark,” “blind,” “benighted,” and “unenlightened.” The images are drawn from situations in which knowledge and its benefits escape us: we are “in a fog” and “clueless.”
The descriptor oblivious is interesting. Its contemporary meaning is “unaware or unmindful of something” or “ignorant of something that is relevant to one’s situation.” This was once considered erroneous usage. The original meaning is “forgetful” or “producing forgetfulness,” derived from the Latin oblivion (“forgetfulness”). The Latin term is itself metaphorical, though what metaphor is involved is controversial: Webster’s Third International Dictionary says its root components (ob + levis) literally meant “to smooth over”; the Oxford English Dictionary (OED) states that it is ultimately derived from a root (lividus) that meant “livid,” a dark or purplish black. In either case, if we once knew something but have forgotten it, it has been smoothed over or gone dark, and we no longer know it. We are, consequently, ignorant of everything we have forgotten.
But this raises a provocative question: do things we have forgotten and things we have never learned have the same epistemic status? They both are things I do not know, yet they seem cognitively different: relearning is different from learning for the first time. Plus, there is the lurking potential that something we have forgotten might one day be remembered. Plato famously taught that all learning is remembering, and he constructed an elaborate myth to explain why all of us had forgotten everything we knew before birth.22 For him, to be ignorant is simply not to remember, to have forgotten. The poetic beauty of this doctrine aside, it is useful to distinguish the “once known” from the “not yet known” in exploring forms of ignorance.
I think of this book as an extended, exploratory essay. As I announced earlier, I have chosen to organize it around four images of ignorance, four spatial metaphors (parts 2–5). Spatial language is commonplace in discourse about knowledge: we speak of “domains” or “fields” of knowledge, “areas” of research or specialization, disciplinary “boundaries,” and so on. My four guiding images are: ignorance as place, boundary, limit, and horizon. They embody clusters of ideas that reflect the ways in which we experience ignorance; revealing the architecture of ignorance, they point to different aspects of the human condition.