I am going to argue for a robust realism about magnitudes, as irreducible elements in our ontology. This realistic attitude, I will argue, gives a better metaphysics than the alternatives. It suggests some new options in the philosophy of science. It also provides the materials for a better account of the mind’s relation to the world, in particular its perceptual relations.

One often hears it said that our visual-perceptual contact with the world is “perspectival.” But this can mean quite different things. Three different senses in which our visual contact with the world is “perspectival” are distinguished. The first involves the detection or representation of behaviorally important relations, holding between a perceiving subject and the world. These include time to contact, body-scaled size, egocentric position, and direction of heading. The second perspective becomes at least explicitly manifest in taking up the “proximal (...) mode” and involves the representation of relational “appearance properties,” such as, perhaps , angular size and angular/projective shape at or from a viewpoint. The third perspective is associated with the pencil of rays structured by the position and geometry of the eyes. The relationships between these three perspectives are charted, and their connection with conscious experiential awareness discussed. So, e.g., there is no simple or direct route from the detection of the relations constitutive of perspective2 to detection of the relations constitutive of perspective1. The relations definitive of perspective3 are probably not themselves detected or represented by the visual system, but define the informational arena within which detection of the relations definitive of perspective1 and perspective2 takes place. (shrink)

If two subjects have phenomenally identical experiences, there is an important sense in which the way the world appears to them is precisely the same. But how are we to understand this notion of 'ways of appearing'? Most philosophers who have acknowledged the existence of phenomenal content have held that the way something appears is simply a matter of the properties something appears to have. On this view, the way something appears is simply the way something appears to be . (...) This identification supports a Russellian theory of phenomenal content, according to which phenomenal content is exhausted by facts about what specific properties are represented by an experience. The present paper motivates and develops an alternative Fregean theory of phenomenal colour content. According to Fregean theories, the phenomenal content that is shared by any two phenomenally identical experiences is a matter of how the world is represented, and need not involve sameness in what is represented. It is argued that ways of appearing are modes of presentations of external properties and objects, and a detailed theory is presented about the nature of the modes of presentation involved in colour experience. (shrink)

Structural realists claim that we should endorse only what our scientific theories say about the structure of the unobservable world. But according to Newman’s Objection, the structural realist’s claims about unobservables are trivially true. In recent years, several theorists have offered responses to Newman’s Objection. But a common complaint is that these responses “give up the spirit” of the structural realist position. In this paper, I will argue that the simplest way to respond to Newman’s Objection is to return to (...) one of the standard motivations for adopting structural realism in the first place: the No Miracles Argument. Far from betraying the spirit of structural realism, the solution I present is available to any theorist who endorses this argument. (shrink)

ABSTRACT According to edenic idealism, our ordinary object terms refer to items in the manifest world—the world of primitive objects and properties presented in experience. I motivate edenic idealism as a response to scenarios where it is difficult to match the objects in experience with corresponding items in the external world. I argue that edenic idealism has important semantic advantages over realism: it is the most intuitive view of what we are actually talking about when we use terms for objects.

ABSTRACTAccording to many naturalists, our ordinary conception of the world is in tension with the scientific image: the conception of the world provided by the natural sciences. But in this paper, I present a critique of naturalism with precedents in the post-Kantian idealist tradition. I argue that, when we consider our actual linguistic behavior, there is no evidence that the truth of our ordinary judgments hinges on what the scientific image turns out to be like. I then argue that the (...) best explanation of this result is that the norms and presuppositions operating in ordinary discourse are different from the norms and presuppositions operating in scientific discourse. So naturalistic attempts to undermine the manifest image are illegitimate attempts to critique a practice ‘from the outside’. (shrink)

I explore two views about the relationship between spatial experience and spatial reality: spatial functionalism and spatial presentationalism. Roughly, spatial functionalism claims that the instantiated spatial properties are those playing a certain causal role in producing spatial experience while spatial presentationalism claims that the instantiated spatial properties include those presented in spatial experience. I argue that each view, in its own way, leads to an ontologically inflationary form of primitivism: whereas spatial functionalism leads to primitivism about phenomenal representation, spatial presentationalism (...) leads to primitivism about spatial properties. I conclude by discussing how to adjudicate between spatial functionalism and spatial presentationalism. (shrink)

The perceptual system estimates distal conditions based upon proximal sensory input. It typically exploits information from multiple cues across and within modalities: it estimates shape based upon visual and haptic cues; it estimates depth based upon convergence, binocular disparity, motion parallax, and other visual cues; and so on. Bayesian models illuminate the computations through which the perceptual system combines sensory cues. I review key aspects of these models. Based on my review, I argue that we should posit co-referring perceptual representations (...) corresponding to distinct sensory cues. For example, the perceptual system represents a distal size using a representation canonically linked with vision and a distinct representation canonically linked with touch. Distinct co-referring perceptual representations represent the same denotation, but they do so under different modes of presentation. Bayesian cue combination models demonstrate that psychological explanation of perception should attend to mode of presentation and not simply to denotation. (shrink)

According to Sparse views of perceptual content, the phenomenal character of perceptual experience is exhausted by the experiential presentation of ‘low-level’ properties such as (in the case of vision) shapes, colors, and textures Whereas, according to Rich views of perceptual content, the phenomenal character of perceptual experience can also sometimes involve experiencing ‘high-level’ properties such as natural kinds, artefactual kinds, causal relations, linguistic meanings, and moral properties. An important dialectical tool in the debate between Rich and Sparse theorists is the (...) so-called ‘method of phenomenal contrast’. I explore how this method of phenomenal contrast interacts with the sort of content-externalism made familiar by Putnam. I show that the possibility of Twin Earth style cases places important restrictions on the range of properties that the method of phenomenal contrast could plausibly apply to. Moreover, these restrictions would apply to some paradigmatically low-level properties as well as to some of the frequently advanced high-level properties. I also draw some general lessons about the different ways one might conceive of the relation between phenomenal character and representational content. (shrink)

Intentionalism is the view that the phenomenal character of a conscious experience is wholly determined by, or even reducible to, its representational content. In this essay I put forward a version of intentionalism that allows (though does not require) the reduction of phenomenal character to representational content. Unlike other reductionist theories, however, it does not require the acceptance of phenomenal externalism (the view that phenomenal character does not supervene on the internal state of the subject). According the view offered here, (...) phenomenal characters essentially represent subject-environment relations that are relevant to the possibilities for causal interaction between the subject and the environment; relations of the kind that J. J. Gibson dubbed affordances. I argue for this view chiefly through an examination of spatial perception, though other cases are also considered. The view assumes that a phenomenal character has an essential functional role; though it need not be assumed that a functional role is sufficient for a phenomenal character. (shrink)

Duration distortions familiar from trauma present an apparent counterexample to what we might call the naive view of duration perception. I argue that such distortions constitute a counterexample to naiveté only on the assumption that we perceive duration absolutely. This assumption can seem mandatory if we think of the alternative, relative view as limiting our awareness to the relative durations of perceptually presented events. However, once we recognize the constant presence of a stream of non-perceptual conscious mental activity, we can (...) provide an attractive, purely relative account of temporal distortions quite consistent with the naive view. I also consider (and reject) a second empirical challenge to the naive view arising from the so-called ‘oddball effect’. I conclude by tentatively pointing to further empirical data, traditionally accounted for in terms of an internal clock model of timing, which, I suggest, may be understood more illuminatingly by appeal to the idea that we perceive duration in part relative to concurrent non-perceptual mental activity. (shrink)

The consensus in contemporary philosophy of mind is that how a perceptual experience represents the world to be is built into its sensory phenomenology. I defend an opposing view which I call ‘moderate separatism’, that an experience's sensory phenomenology does not determine how it represents the world to be. I argue for moderate separatism by pointing to two ordinary experiences which instantiate the same sensory phenomenology but differ with regard to their intentional content. Two experiences of an object reflected in (...) a mirror can possess the same spatial phenomenology while representing that object to occupy different spatial locations. So, contrary to the current consensus, the representation of spatial location is not fixed by an experience's sensory phenomenology. (shrink)

The reports of individuals who have had their vision restored after a long period of blindness suggest that, immediately after regaining their vision, such individuals are not able to recognize shapes by vision alone. It is often assumed that the empirical literature on sight restoration tells us something important about the relationship between visual and tactile representations of shape. However, I maintain that, immediately after having their sight restored, at least some newly sighted individuals undergo visual experiences that instantiate basic (...) shape phenomenology but which do not present (that is, neither represent nor involve acquaintance with) the corresponding shape properties. Consequently, the empirical literature on sight restoration tells us something important about the role that perceptual phenomenology plays in our perceptual awareness of an object’s properties—it tells us that the properties presented by perceptual experiences are not determined by or “built into” perceptual phenomenology. In addition, I maintain that the evidence concerning sight restoration suggests an alternative theory concerning the role that sensory phenomenology plays in our perceptual awareness of an object’s properties. Specifically, it suggests that, while not inherently representational, sensory phenomenal properties can serve as vehicles for the representation of an object’s properties. (shrink)

Representationalism is, roughly, the view that experiencing is to be analyzed wholly in terms of representing. But what sorts of properties are represented in experience? According to a prominent form of representationalism, objective representationalism, experiences represent only objective (i.e. suitably mind-independent) properties. I explore subjective representationalism, the view that experiences represent at least some subjective (i.e. suitably mind-dependent) properties. Subjective representationalists, but not objective representationalists, can accommodate cases of illusion-free phenomenal inversion. Moreover, subjective representationalism captures the so-called transparency of experience, (...) as it is standardly articulated, just as well as objective representationalism. (shrink)

Despite the fact that many of our beliefs are justified by perceptual experience, there is relatively little exploration of the connections between epistemic justification and perceptual content. This is unfortunate since it seems likely that some views of justification will require particular views of content, and the package of the two might be quite a bit less attractive than either view considered alone. I will argue that this is the case for epistemic internalism. In particular, epistemic internalism requires a view (...) of perceptual content that results in an error theory of perception. This, in turn, hobbles the internalist’s account of perceptual justification. While there are various stages along the way at which one can resist the argument, each one will involve significant commitments that highlight heretofore unacknowledged connections between justification and content. Even if the internalist is willing to make these moves and resist the argument, the argument reveals a novel way for the epistemic externalist to resist one of internalism’s main arguments. (shrink)

The ability to perceive the shapes of things as enduring through changes in how they stimulate our sense organs is vital to our sense of stability in the world. But what sort of capacity is shape constancy, and how is it reflected in perceptual experience? This paper defends a pluralist account of shape constancy: There are multiple kinds of shape constancy centered on geometrical properties at various levels of abstraction, and properties at these various levels feature in the content of (...) perceptual experience, governing patterns of apparent shape similarity. I propose that the varieties of shape constancy are subserved by the syntactic complexity of perceptual shape representations. By assigning discrete constituents to various abstract shape parameters, these representations attune us to the preservation of certain abstract shape properties through changes in more determinate shape properties. Finally, I draw broader lessons concerning the nature and function of perceptual constancy. (shrink)

There is an ongoing debate in philosophy of mind and epistemology about whether perceptual experience only represents those “thin” features of our environment that are apprehended by our senses, or whether, in addition to these, at least some perceptual experiences represent more complex, “thick” properties. My aim in this paper is to articulate an important difference between thin and thick properties, and thus to diagnose a key intuitive resistance many proponents of the thin view feel towards the thick view. My (...) diagnosis then provides us with a novel and compelling argument against the thick view. In what follows, first I consider two unsuccessful versions of an alternative strategy against the thick view found in the literature. Next, I present my own argument. The argument involves proposing two constraints on the phenomenal contents of perceptual experience, which I call the Presentation Principle and the Containment Principle, and then reasoning from these principles to a conclusion that is fatal to the thick view—an outcome that I call the problem of Phenomenal Explosion. I conclude by responding to several objections. (shrink)

According to a number of popular intentionalist theories in philosophy of mind, phenomenology is essentially and intrinsically intentional: phenomenal properties are identical to intentional properties of a certain type, or at least, the phenomenal character of an experience necessarily fixes a type of intentional content. These views are attractive, but it is questionable whether the reasons for accepting them generalize from sensory-perceptual experience to other kinds of experience: for example, agentive, moral, aesthetic, or cognitive experience. Meanwhile, a number of philosophers (...) have argued for the existence of a proprietary phenomenology of thought, so-called cognitive phenomenology. There are different ways of understanding the relevant sense of “proprietary,” but on one natural interpretation, phenomenology is proprietary to thought just in case enjoying an experience with that phenomenal character is inseparable from thinking an occurrent, conscious thought. While one may have instances of thought without CP experience, one will never find CP independent of thought. So the former justifiably can be said to “belong to” the latter. The purpose of this paper is to argue that these intentionalist and cognitive phenomenology views make surprisingly uncomfortable bedfellows. I contend that the combination of the two views is incompatible with our best theories of how our concepts are structured. So cognitive phenomenology cannot determine the contents of our thoughts. (shrink)

According to Minkoswki, Einstein's special theory of relativity reveals that ‘space by itself, and time by itself are doomed to fade away into mere shadows’. But perceptual experience represents objects as instantiating shapes like squareness — properties of ‘space by itself’. Thus, STR seems to threaten the veridicality of shape experience. In response to this worry, some have argued that we should analyze the contents of our spatial experiences on the model of traditional secondary qualities. On this picture—defended in recent (...) work by Chalmers —an experience of squareness just represents whatever property usually causes such experiences. This view salvages the veridicality of shape experience, but leaves the nature of the properties we perceive outside our ken. I argue that such a move is unwarranted: STR is compatible with the idea that shape experience acquaints us with the spatial character of our world. In defending this claim, I propose a view on which shape experience presents familiar Euclidean spatial properties veridically, while implicitly representing those properties as instantiated in a particular manner — namely, relative to our own frame of reference. (shrink)

We motivate five constraints on theorizing about sensory experience. We then propose a novel form of naturalistic intentionalism that succeeds where other theories fail by satisfying all of these constraints. On the proposed theory, which we call structure matching tracking intentionalism, brains states track determinables. Internal structural features of those states select determinates of those determinables for presentation in experience. We argue that this theory is distinctively well-positioned to both explain internal-phenomenal structural correlations and accord external features a role in (...) fixing phenomenology. In addition, we use the theory to shed light on how one comes to experience “missing shades”. (shrink)

In recent work, David Chalmers argues that “Edenic shapes”—roughly, the shape properties phenomenally presented in spatial experience—are not instantiated in our world. His reasons come largely from the theory of Special Relativity. Although Edenic shapes might have been instantiated in a classical Newtonian world, he maintains that they could not be instantiated in a relativistic world like our own. In this essay, I defend realism about Edenic shape, the thesis that Edenic shapes are instantiated in our world, against Chalmers’s challenge (...) from Special Relativity. I begin by clarifying the notion of an Edenic shape by reference to Chalmers’s notion of the “Edenic” content of perceptual experience. I then reconstruct Chalmers’s argument that Edenic shapes could not be instantiated in a relativistic world. His reasoning proceeds from two assumptions. The first is that the only shape properties instantiated in a relativistic world are those which somehow involve relations to frames of reference. This is thought to follow from the phenomenon of Lorentz contraction, a consequence of Special Relativity. The second assumption is that Edenic shapes do not involve relations to frames of reference. One reason to accept the second assumption is that it seems that Edenic shapes could be instantiated in a classical Newtonian world, where the notion of a frame-relative shape has no meaningful application. I then proceed to defend RES against Chalmers’s argument by arguing that Special Relativity, properly understood, provides no support for Chalmers’s first assumption. More generally, I argue, by way of a careful analysis of the geometric structure of Minkowski space–time and Galilean space–time Newtonian physics), that Edenic shapes are no less at home in a relativistic world than in a classical Newtonian world. (shrink)

Imagine your mirror‐inverted counterpart on Mirror Earth, a perfect mirror image of Earth. Would her experiences be the same as yours, or would they be phenomenally mirror‐inverted? I argue, first, that her experiences would be phenomenally the same as yours. I then show that this conclusion gives rise to a puzzle, one that I believe pushes us toward some surprising and philosophically significant conclusions about the nature of perception. When you have a typical visual experience as of something to your (...) left, the following three claims seem very plausible: (1) No one could have an experience phenomenally just like yours without thereby having an experience as of something to her left. (2) Your experience is veridical. (3) Your experience doesn't differ from that of your mirror‐inverted counterpart with respect to veridicality. But (1)‐(3) jointly contradict the claim that you and your mirror‐inverted counterpart would have the same experiences. I argue that any viable response to this puzzle will embrace the following disjunction: either there is a degree of independence between perceptual phenomenology and representational content, contrary to popular intentionalist views of perception, or spatial subjectivism is true, where spatial subjectivism is the view that the spatial properties presented in perception are either mind‐dependent or illusory. (shrink)

In what sense does empty space feature in visual experience? In the first part of this essay I sketch a view advanced by Soteriou and Richardson on which one's visual awareness of empty space is explained by appeal to ‘structural’ features of the phenomenology of visual experience, in particular the phenomenology of experiencing one's visual field as bounded. I suggest that although this ‘structuralist’ view is silent on whether empty space has a phenomenal appearance, the very appeal to structural features (...) seems a natural foil to some such thought. In the second part, I outline a view on which it can be granted that empty space does, after all, have a phenomenal appearance and, so, is not best cast as a species of absence perception as the structuralist avows, at least on a certain construal of ‘absence perception’. After O'Shaughnessy , I contend that although some privations have a phenomenal appearance, ‘absence perception’ should single out the putative perception of phenomena that lack phenomenal reality. I finally consider how the descriptive phenomenology that the structuralist points to, and which I urge should be embraced, can nonetheless be reconciled with the view I spell out. (shrink)

I present a novel anti-sceptical BIV argument by focusing on conditions on the production and use of the locative preposition ‘in’. I distinguish two uses of ‘in’—material and descriptive phenomenological—and I explain in what respect movement is central to the concept that our use of ‘in’ expresses. I go on to argue that a functionalist semantics of the intelligible use of ‘in’ demands a materialist philosophy of action in the spirit of G.E.M. Anscombe, but also why the structure of space (...) is not irrelevant either; appeal to the structure of space unsettles the causal-empirical assumptions that ground the picture of subjectivity and agency that the biv narrative assumes. Finally, I explain why a functionalist semantics demands a Naïve Realist metaphysics of perception, consistent with some of Putnam’s last writings on philosophy of perception. (shrink)

This is a reply to commentaries on my book, The Character of Consciousness, by Benj Hellie, Christopher Peacocke, and Susanna Siegel. The reply to Hellie focuses on issues about acquaintance and transparency. The reply to Peacocke focuses on externalism about spatial experience. The reply to Siegel focuses on whether there can be Frege cases in perceptual experience.

Malebranche holds that visual experience represents the size of objects relative to the perceiver's body and does not represent objects as having intrinsic or nonrelational spatial magnitudes. I argue that Malebranche's case for this body-relative thesis is more sophisticated than other commentators—most notably, Atherton and Simmons —have presented it. Malebranche's central argument relies on the possibility of perceptual variation with respect to size. He uses two thought experiments to show that perceivers of different sizes—namely, miniature people, giants, and typical human (...) beings—can experience the very same objects as having radically different sizes. Malebranche argues that there is no principled reason to privilege one of these ways of experiencing size over the others and, more specifically, that all three kinds of perceivers experience size veridically. From the possibility of this kind of veridical perceptual variation, Malebranche infers that visual experience represents only body-relative size. (shrink)

A coin rotating back in depth in some sense presents a changing, elliptical shape. How are we to understand such (in this case) ‘appearances of ellipticality’? How is the experiential sense of such shifting shape appearances related to the experiential sense of enduring shape definitive of perceived shape constancy? Is the experiential recovery of surface shape based on the prior (perhaps more fundamental) recovery of point or element 3D spatial locations?—or is the perception of shape a largely independent perceptual achievement? (...) Do we gain access to enduring shape properties by first detecting and working from ‘shape appearances’? These are some of the topics taken up in this paper. (shrink)

An empirically based view of size and distance perceptual content and phenomenology is introduced, in which perceivers measure worldly size and distance against their bodies. Central principles of the formal, representational theory of the measurement of extensive magnitudes are then applied in framing the account in a precise way. The question of whether spatial-perceptual experience is “unit-free” is clarified. The framework is used to assess Dennis Proffitt's proposal that spatial setting is perceived in various “units,” “scales,” or “rulers”, some of (...) them non-spatial—distance in terms of calories burned to traverse and the like. The debate between Proffitt and Firestone about the commensurability of differing measurement scales held by Proffitt to be relied on by perceivers is then clarified and resolved. Finally, the measurement theory framed account of size and distance perception is used to illuminate Gibson’s famous but elusive contrasts between “geometrical optics” and “ecological optics” and between the “physical world” and the “animal environment”. (shrink)

I develop a Russellian representationalist account of size experience that draws importantly from contemporary vision science research on size perception. The core view is that size is experienced in ‘body-scaled’ units. So, an object might, say, be experienced as two eye-level units high. The view is sharpened in response to Thompson’s (forthcoming) Doubled Earth example. This example is presented by Thompson as part of an argument for a Fregean view of size experience. But I argue that the Russellian view I (...) develop handles the Doubled Earth example in a natural and illuminating way, thereby avoiding the need to posit irreducible experiential ‘modes of presentation’. I also address a kind of neo-Fregean ‘reference-fixing’ view of size experience, that shares features with the Russellian view developed. I give reasons for favoring the latter. Finally, I argue that Peacocke’s claim that spatial experience is ‘unit free’ is not persuasive. (shrink)

Liberals about perceptual contents claim that perceptual experiences can represent kinds and specific, familiar individuals as such; they also claim that the representation of an individual or kind as such by a perceptual experience will be reflected in the phenomenal character of that experience. Conservatives always deny the latter and sometimes also the former claim. I argue that neither liberals nor conservatives have adequately appreciated how the content internalism/externalism debate bears on their views. I show that perceptual content internalism entails (...) conservativism when conjoined with one other, extremely plausible premise. Hence, liberals are committed to perceptual contents externalism, yet they have failed to fully address the consequences that this has for their view. Moreover, the argument is easily adapted to perceptual experiences of Twin Earthable properties, like colour and shape. I use this last result to show why existing conservative arguments that appeal to Twin Earth plausibly overgeneralize. (shrink)

In the present paper, the notion that brains in vats with perceptual experiences of the same type as ours could perceptually represent other entities than shapes is challenged. Whereas it is often held that perceptual experiences with the same phenomenal character as ours could represent computational properties, I argue that this is not the case for shapes. My argument is in brief that the phenomenal character of a normal visual experience exemplifies shapes – phenomenal shapes – which functions as the (...) vehicle for our perceptual representation of shapes. Due to the unique mereological structure of shapes, phenomenal shapes are unable to reliably track any property but shapes. In so far as reliable tracking is a necessary condition for perceptual representation, phenomenal shapes can consequently and contrary to received wisdom only represent shapes. (shrink)

This paper presents a framework for analysing perceptual Twin Earth thought experiments. Visual content normally has an analogue character, and it is argued in this paper that this sets certain constraints on the extent to which Twin Earth thought experiments can be successful. The argumentation in the paper is developed by using examples from visual spatial content. It is argued that visual spatial content can only be “twin-earthed” in a very limited way. Whereas the metrics of space can be twin-earthed, (...) visual experience has a structure that means that it can only be the vehicle for representing entities with geometrical structures. (shrink)

This paper is a defense of an internalist view of the perception of shapes. A basic assumption of the paper is that perceptual experiences have certain parts which account both for the phenomenal character associated with perceiving shapes—phenomenal shapes—and for the intentional content presenting shapes—intentional shapes. Internalism about perceptions of shapes is defined as the claim that phenomenal shapes determine the intentional shapes. Externalism is defined as the claim that perceptual experiences represent whatever shape the phenomenal shape reliably tracks. The (...) argument against externalism proceeds in three steps. First, it is argued that phenomenal shapes are modality specific, such that a phenomenal shape that features in a visual perceptual experience cannot feature in a haptic perceptual experience, and vice versa. Second, it is argued that intentional shapes are amodal. Third, it is argued that externalism is incompatible with the fact that phenomenal shapes are modality specific and intentional shapes amodal. (shrink)

The thesis is intended to contribute to the growing understanding of the indispensable role played by phenomenal consciousness in human cognition, and specifically in making our concepts of the external world available. The focus falls on so called observational concepts, a type of rudimentary, perceptually-based objective concepts in our repertoire — picking out manifest properties such as colors and shapes. A theory of such concepts gets provided, and, consequently, the exact role that perceptual consciousness plays in making concepts of this (...) sort available gets settled. In the first half of the thesis, observational concepts get construed as a special type of recognitional concepts. On an analogy with perceptual demonstratives, having such concepts would involve having non-trivial knowledge of their reference. The experiential basis of such concepts would, among other things, provide for such constitutive knowledge. The theoretical background relevant to the hypothesis gets provided in the first chapter. A defence of the hypothesis follows in the second. In the second half of the thesis, care is taken to distinguish among two ways in which the constitutive knowledge of the reference of an observational concept could be fleshed out. In the third chapter, perceptual experience is shown to provide the basis both for knowledge of observational properties by acquaintance, and for knowledge of the essence of such properties — provided that knowledge of essence gets construed in the right, modest way. It might be natural to take knowledge by acquaintance to be the sort relevant to observational concept possession, especially given that in the case of perceptual demonstratives this is the role likely played by experience. However, this initial impression proves to be mistaken. The constitutive knowledge of the referent of an observational concept turns out to consist in the capacity to determine a priori the essence of the respective property. To show this, an argument gets provided in the penultimate fourth chapter, based on the key role played by experiences of instances of observational properties in optimal viewing conditions in enabling the possession of the respective observational concept. (shrink)