Consider each in order. Negative data as negative evidence.
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To support this claim, nativists almost always cite one particular study: Brown and Hanlon For example, Hirsh-Pasek, Treiman, and Schneidermann found that two year olds had their ill-formed utterances repeated by their mothers with significantly more frequency than their well-formed sentences and, further, that these repetitions also corrected the child's error. The author also briefly summarizes the research of Demetras, Post, and Snow and Bohannon and Stanowicz which also provides evidence that feedback to children is provided differentially for their ill-formed vs. However, before finishing her discussion of this topic, the author presents, and then responds to, some of criticisms leveled at the aforementioned research.
The first criticism she examines is that provided by Morgan and Travis They examined Brown's original data, generating findings in general agreement with the aforementioned researchers. For example, Morgan and Travis found that, for all the children in the study, expansions followed ungrammatical utterances with greater frequency than they followed grammatical utterances.
According to them, for negative evidence to be effective, it must be supplied with much greater frequency and over a longer time. In supporting her point, the author quotes Demetras, Post, and Snow , p. In addition to the critique of Morgan and Travis, the author summarizes that of Marcus The author begins by reporting Marcus' observation that children with differing familial and cultural backgrounds receive diverse types and amounts of feedback.
Yet, despite these differences, virtually all children master their native tongue. Thus, for Marcus, there appears to be no evidentiary support for claiming that feedback is required for language mastery.
For example, based on the type of feedback reported in Bohannon and Stanowicz , Marcus contends that a learner would need to repeat any given string 85 times and receive feedback as described by Bohannon and Stanowicz to reach 99 percent certainty regarding its grammatically. However, since children become reasonably adept at grammatical well-formedness without such repetitions, Marcus concludes that the role played by feedback is not crucial.
The author finds support for her view from others. For example, MacWhinney , p. The author also takes issue with Marcus' second criticism. Thus, the logical problem is resolved without invoking nativism. Positive data as negative evidence. Based on Pinker , the author offers what the former calls constraint sampling as a method for utilizing positive data to correct grammatical errors.
In constraint sampling, the learner is viewed as randomly picking one feature of a sentence appearing in the primary linguistic data and then using that feature as a constraint. Consider the following example of how a language learner might come to learn to attach the suffix s to a verb stem when forming a declarative sentence. Assume that the learner hears the sentences The boy wants a curry and Dad wants a beer, yielding the general rule that a verb stem should always have an s attached to it. According to the author's account of constraint sampling, the learner would immediately hypothesize a constraint of this rule—perhaps, that one adds s when the subject of the declarative sentence is animate.
This rule would be falsified by exposure to a sentence such as The curry tastes good, at which point the learner might hypothesize that s is used for the present tense.
Here the learner used positive data—exposure to the sentence The curry tastes good —as negative evidence to correct her earlier overgeneralization. In this manner a learner ultimately forms a rule with the appropriate constraints the author, p. Of course, unlike Pinker who is a nativist , the author sees constraint sampling and constraint setting as a product of prior experience. Nonoccurrence as negative evidence. According to the author, some e. For example, in addition to uttering grammatically correct sentences such as I melted it, this learner says, incorrectly, I giggled her when she means that she caused her to giggle.
Now suppose this learner sees her father knock his coffee off the table. If her father speaks on the matter e. Instead, she hears her father say I caused the cup to fall from the table. The nonoccurrence of I falled the cup off the table provides negative evidence for her faulty rule that all intransitive verbs can serve as causatives the author also notes that hearing I caused the cup to fall from the table constitutes positive data serving as negative evidence for the faulty rule.
Consider these two strings: According to the author, the nonoccurrence of the first string does not constitute negative evidence that it is ill-formed, while the nonoccurrence of the second string does constitute evidence of its ill-formedness. In explaining this distinction, the author first differentiates between a string qua string and a string qua instance of a particular syntactic structure. For any given syntactic structure, there are many strings to which a learner has been exposed.
So, although Steve enjoyed the curry may not have been uttered in the learner's presence, many other strings exhibiting its structure e. Hence, the nonoccurrence of any particular string is not evidence that it is ill-formed, since many other strings with its structure are part of the learner's primary linguistic data. This is not the case, the author argues, for the nonoccurrence of Enjoy the curry Steve the. For the nativist, it is not possible. However, this information is not available in the environment in a form accessible to a pre-linguistic child. Therefore, the UG must be innately given.
For example, within Chomsky's principles and parameters approach, the UG provides knowledge of the what is called the pro-drop parameter. Specifically, prior to learning a language, the child somehow already knows that some languages allow sentences lacking apparent subjects null-subject languages , others non-null-subject languages do not.
English is an example of the former, Italian the latter. How the parameter is set then governs a learner's future grammatical constructions. The author, however, raises serious objections to Chomsky's assertion that the UG exists, and thereby objects to the iterated poverty of the stimulus argument. Consider again the pro-drop parameter. The author cites Hyams as observing that virtually all children initially speak as if their language is a null-set language.
Is the correct setting triggered by the positive data available in adult speech? If that is the claim, then UG proponents have to account for the fact that much of the positive data in English contains null-set sentences Berman, The author offers the following examples: Couldn't give a damn, Wouldn't believe a word he said, and Must have been the mailman p. If the existence of the UG is questionable, then, for the author, an empiricist is not burdened with having to explain how it is acquired.
Hyperbole aside, my purpose was to emphasize the no-holds-barred nature of the disagreement between the author and some linguistic nativists. This conflict is particularly well represented in the polemical style exhibited by both sides. Of course, the other side has been equally combative in its rhetoric. In this review I have not added to these criticisms by providing a behavior-analytic critique of her book.
Rather, my intent has been to furnish behavior analysts with an exposition of one philosopher's often-elaborate critique of three versions of the POSA. This critique after a suitable behavior-analytic translation is largely congenial with a behavior-analytic perspective on language acquisition and thus provides behavior analysis with additions to its armamentarium of arguments. Given this concern, behavior analysis can take its lead from philosopher Richard Rorty e.
Davidson, do not consider themselves pragmatists. The upshot of this approach for Rorty has been, in addition to successfully promoting neo-pragmatism, the encouragement of a productive dialogue with those from whom he has borrowed. Perhaps the same can happen between Cowie and behavior analysts. Indeed, Cowie's statements regarding behaviorism—e.
The product of such exchanges between behavior analysts and Cowie, as well as exchanges with others outside behavior analysis who also offer critiques of nativism e. In this book review I quote copiously from the book. Any given paragraph frequently contains a number of quotes from a specific page. To promote easier reading, such paragraphs generally cite the page number s for these quotes only once.
National Center for Biotechnology Information , U. Journal List Anal Verbal Behav v. Stanislaus County Office of Education. Address correspondence to Ted Schoneberger, P. Box , Turlock, CA ; e-mail: This article has been cited by other articles in PMC. Abstract In What's Within? Nativism Reconsidered , the author, philosopher Fiona Cowie, addresses three principle questions: An Historical Overview The author p. The Five Core Claims According to the author pp. Representationalism Characterized by the author p. Domain Specificity For Chomsky, some of the constraints placed upon our cognitive capacities by our biology are domain neutral.
Universal Grammar UG As previously stated, the UG, under current Chomskyan theory, is comprised of principles and parameters operative for all human languages. The A Posteriori Poverty of the Stimulus Argument Although all five core claims are constitutive of Chomskyan nativism, particular attention has been paid by his critics to domain specificity, innateness, and universal grammar.
Syntactic theory and the projection problem. In defense of development. Behavioral and Brain Sciences. The issue of negative evidence: Adult responses to children's language errors. On two types of models of the internalization of grammars. The ontogenesis of grammar: Brown R, Hanlon C. Derivational complexity and order of acquisition in child speech.
Cognition and the development of language. Aspects of the theory of syntax. Its nature, origin, and use. Language and problems of knowledge: Linguistics and cognitive science: Government and binding theory and the minimalist programme. Current thoughts on ancient problems part 1 Retrieved October 10, , from http: Cowie on the poverty of stimulus.
Oxford University Press; Retrieved October 10, , from http: Language acquisition in the absence of experience. Crain S, Thornton R.
Recharting the course of language acquisition: Studies in elicited production. Biobehavioral foundations of language development. Inquiries into truth and interpretation. Feedback to first language learners: The role of repetitions and clarification questions. Journal of Child Language. A connectionist perspective on development. Doing without what's within; Fiona Cowie's critique of nativism.
Complexity and the function of mind in nature. Cambridge University Press; Brown and Hanlon revisited: Mothers' sensitivity to ungrammatical forms. Stanford Linguistics Association; The pro-drop parameter in child grammars. Toward a biology of grammars. The teachability of language. The child's construction of grammatical categories. Wanner E, Gleitman L.
The state of the art. Negative evidence in language acquisition. Positive evidence for negative evidence. Limits on negative information in language input. Maternal input adjustments and non-adjustments as related to children's linguistic advances and to language acquisition theories. The development of oral and written language in social contexts. Some effects and non-effects of maternal speech style. Language input and acquisition.
Productivity and conservatism in language acquisition. Demopoulos W, Marras A, editors. Language learning and concept acquisition: How the mind creates language. Language acquisition in the absence of proof of absence of experience. Learnability, hyper-learning, and the poverty of the stimulus. Johnson J, Luge M. Proceedings of the 22nd annual meeting: General session and parasession on the role of learnability in grammatical theory. Berkeley Linguistics Society; The philosophy of language.
Read C, Schreiber P. Why short subjects are harder to find. Philosophy and social hope. Statistical learning by 8-month-old infants. A Departure from cognitivism: Implications of Chomsky's second revolution in linguistics. The Analysis of Verbal Behavior. Sense data theorists have often held it to be intuitively obvious that when we are directly, perceptually aware of something, that thing must have the properties that it appears to have Price , p. Opponents of sense data have typically found this assumption unmotivated; J. Austin, the best-known critic of the argument from illusion and related arguments for sense data, is a case in point:.
Austin's point seems to be that, just as a church can merely look like a barn without there being anything that is a barn, the table that we see in Hume's example may merely seem to get smaller, without there being anything that actually gets smaller. Modifications might be made to this argument to make it more plausible: Something like this argument may be what Hume had in mind, if only implicitly.
Critics of this version of the argument may question either premise. Thomas Reid seems to deny premise 8 , arguing that the external object changes in respect of certain relational properties. For instance, when one moves farther away from a table, the table's angular size relative to one's own position decreases, where this is the size of the angle created by connecting the extremities of the table to the point in space from which the table is viewed. Though this property is relational, the relationship involved is a purely physical one, holding between physical things such as the table and the eye, so it might be said that there is no need to introduce mind-dependent sense data as objects of awareness Reid , pp.
The Argument from Illusion is the best-known and most historically influential argument for the existence of sense data. An illusion is a case in which one perceives an object, but the object is not the way it appears in some respects. For instance, when one views a straight stick half-submerged in water, the stick may appear bent. Since it is not in fact bent, this is an illusion. Some philosophers have argued that the possibility of such sensory illusions shows that what we are directly aware of in perception is never the real, physical object Ayer , pp.
Using the bent-stick illusion as an example, one might argue:. A background assumption is that there is only one stick-like thing that one sees in the example, and that thing is either an actual, physical stick, or a sense datum of a stick. The argument concludes that it is not the physical stick, so it must be a sense datum. Step 4 seems plausible, since one can imagine first perceiving the stick normally, and then moving it into the water. It would be implausible to maintain that one is seeing the physical stick up to the moment when it touches the water, at which point the object of one's awareness suddenly changes to a sense datum.
Opponents of sense data object to premise 1 on grounds similar to those considered in section 2. Sense data theorists and their opponents, again, disagree over whether an object of direct awareness must have exactly the features it appears to have. Having been taken to task by Austin over the argument from illusion, A. Ayer sought to defend sense data by another argument though Ayer seems to think it is the same argument:. Ayer's central premise seems to be that all such beliefs about the physical world are fallible; somehow, this is supposed to force the conclusion that such beliefs are inferential.
That, in turn, is supposed to support the sense data theory. Conclusion 5 does not suffice to establish the existence of sense data, but by ruling out the competing direct realist theory, it would take Ayer a considerable distance towards vindicating the sense data theory. If beliefs about sense data could plausibly be claimed to be infallible, and if one assumes a foundationalist epistemology, beliefs about sense data would be prime candidates for constituting non-inferential knowledge.
This would make sense data very plausible candidates for objects of direct awareness. Unfortunately, Ayer gives no motivation for premise 2 , which is rejected by most contemporary foundationalists Audi ; Alston ; Huemer , pp. A hallucination is a case in which one has an experience qualitatively like perception, but there is no external object that one is perceiving. For instance, a large dose of LSD might cause me to have an experience of seeming to see a pink rat on this table, where there is in reality nothing pink-rat-like. Some believe that the possibility of hallucinations shows that even normal perception always involves sense data Robinson , pp.
Imagine two people, Sally and Sam, each of whom is having an experience of seeming to see a pineapple. Sally is simply perceiving a pineapple in the normal way. Sam, however, is having an incredibly realistic hallucination of a pineapple, induced by brain scientists who have sophisticated technology for electrically stimulating Sam's brain. And suppose, as is theoretically possible, that the brain state causally relevant to Sally's visual experience is the same as the brain state causally relevant to Sam's visual experience. I will call this brain state B. Sam would be unable to distinguish his experience from a normal perception of a pineapple.
In this scenario, what is Sam directly aware of? Surely not a physical pineapple, since no physical pineapple is present. It seems, then, that he must be aware of a mere mental image of a pineapple. This mental image is caused by brain state B. Now, what about Sally? Sally's brain state was caused in a different way from Sam's — Sally's was caused by a real pineapple, whereas Sam's was caused by the brain scientists.
But that does not change the fact that Sally is now in the same brain state as Sam. We have already said that in Sam, brain state B caused a mental image of a pineapple. Therefore, it seems that if someone else were to have state B, it would also cause a mental image of a pineapple for them. Therefore, it seems that Sally must also be having a mental image of a pineapple, since she is in state B. Therefore, normal perception involves sense data, just as hallucination does. This argument relies on the principle that, if a causal chain of events leads to some effect, E, then any series of events that duplicates the last member of the causal chain will also produce E, regardless of whether the earlier members of the chain are duplicated.
As long as Sally and Sam get into the same brain state, regardless of how they got there, both should experience whatever effects result from that brain state. One way for a critic of sense data to respond to this argument would be to deny that state B causes Sam to have a mental object of awareness. According to the intentionalist account of perception, what Sam has is a mental state that falsely represents there to be a pineapple. Sally also has a mental state that represents there to be a pineapple, though in her case the representation is true.
It may be held that Sam's mental state has no object of awareness since it is entirely false, whereas Sally's mental state has the physical pineapple as its object of awareness. Thus, in neither case must we posit a mental object of awareness, as in the sense data theory Huemer , pp. Hume tells us that one can induce a case of double vision in oneself by merely pushing on one eye with one's finger. The possibility of double vision, he believes, shows that the immediate objects of awareness in perception are not the real, physical objects Hume , I.
The intended argument may be something like this:. It would be implausible to maintain that one of the two things is a sense datum while the other is a real object. Therefore, one should conclude that both of the things one sees are sense data, rather than physical objects. Critics might respond to this argument by claiming that in a case of double vision, rather than seeing two things, one sees a single thing that merely appears to be in each of two places Huemer , pp.
There is always a time delay between any event in the physical world and our perception of it. The star responsible for Sally's experience still exists. But the star ultimately responsible for Sam's experience ceased to exist years ago. What is Sam directly aware of? Surely not an actual star, since no star presently exists in the place where he is looking.
It must be a mere mental image of a star that he is directly aware of. Just as in the case of the argument from hallucination, we can now argue that since Sally is in the same brain state as Sam, she must also be having a mental image of a star. Therefore, sense data are involved in normal perception, even when the physical object responsible for the perception still exists.
Russell , p. One might be tempted to say that what Sam sees is light rays , rather than a sense datum. But if the time gap shows that Sam does not directly perceive the star, it must also show that Sam does not directly perceive anything else outside of him either, since there is some time delay, however small, between any external event and Sam's corresponding sensory experience.
Sam's visual experience as of a star will occur at least slightly later than the light rays strike his retina. Consider the case of colors. A sense data theorist might argue:. See Russell , pp. The first premise seems obvious on its face. The second premise may seem unbelievable, but there are several arguments for it.
One of these arguments appeals to differences of color perception among people. Not only color blind people, but even people with normal vision differ among themselves slightly in how they perceive the colors of things Hardin , pp. If colors are really out there, then there would have to be an answer to the question, Whose color perceptions are right? But not only is there no way of determining the answer to that; it seems hard to think of what facts might make one person's color perceptions more correct than another's.
A related argument appeals to the differences of color perception among different species of animals on these differences, see Jacobs , chapter 5; Varela et al. Again, there seems no answer to the question of which species is right. Another argument appeals to the fact that our experiences of color are caused by the wavelengths of light that physical objects reflect. Therefore, it seems that if colors belong to physical objects, they must be reducible to spectral reflectance distributions as Byrne and Hilbert  claim.
However, there is in general no single spectral reflectance distribution, or even a single continuous range of spectral reflectance distributions, corresponding to each of the colors we see. Two objects with very different spectral reflectance distributions may both appear orange to us in normal lighting conditions, for example. Some philosophers hold that colors are dispositions to cause certain kinds of sensory experiences in us, rather than dispositions to reflect light in certain ways. But others object that this is not so, because colors ought to be properties that we directly perceive things to have, whereas we do not perceive things as having dispositions to cause experiences in us.
There is a good deal to be said about color, and a good deal yet to be resolved. The ultimate acceptability of premise 2 of the above argument will turn on whether some reductive theory of the nature of colors is defensible. One reason the sense data theory has lost favor is no doubt the ascendance of physicalism in the philosophy of mind.
Physicalists believe that the world is entirely physical; in particular, they believe that mental states either do not exist or are reducible to physical states, such as brain states. For various reasons, most contemporary thinkers in philosophy of mind embrace some form of physicalism and reject dualism. If they are right to do so, then there is a reason for rejecting sense data: Sense data are supposed to have the properties that perceptually appear to us.
But, in cases of normal perception, the only physical things that have the properties that perceptually appear to us are the external objects that the direct realists say we are perceiving; and in cases of illusions and hallucinations, there are no physical things that have the properties that perceptually appear to us. In particular, our brain states manifestly do not ordinarily have the properties that perceptually appear to us except in the odd case that we happen to be looking at a brain. So sense data, if they exist, must be non-physical things.
Presumably he would draw a similar distinction for other properties of the sense-datum. His view seems to be that sense data might be identical with brain states, so that the sense data one experiences would in fact have the properties, such as shape, location, and perhaps color, of one's brain states, even though they are given experientially as having different and incompatible sets of properties.
O'Shaughnessy does not explain what it is for a thing to be given experientially as having a property, but he seems to be abandoning the traditional doctrine that sense data literally have the features that perceptually appear to us. A more perspicuous response to the argument from physicalism is to simply embrace mind-body dualism Jackson At least three sorts of epistemological objections to the sense data theory have been raised.
The first and most common charge is that the sense data theory leaves us vulnerable to external world skepticism. If we are only ever directly aware of our own sense data and other nonphysical phenomena, it is said, then it is unclear what reason we have for believing anything physical exists. Sense data theorists will generally admit that it is logically possible that someone should have exactly the same sense data that I, for example, have, and yet for there to be no physical objects around that person of the kind that I take myself to be surrounded by.
Berkeley , section 20 famously took this point to show that I have no good reason for believing in such physical objects. However, as Jackson , pp. To rule this out, one may appeal to Hume's , XII. On this view, in order to non-demonstratively infer any conclusion about physical objects, one must first have past experience of physical objects from which one might draw generalizations. If, as the sense data theory holds, one's immediate experience only ever concerns sense data, then one's inductive inferences can only draw generalizations about sense data.
Sense data theorists can respond to this skeptical challenge by proposing that our beliefs about the physical world are justified by inference to the best explanation Jackson , pp. Similarly, perhaps we know of the existence of physical objects in general, despite never having directly observed one, because the theory that posits physical objects provides the best explanation for other things that we know about the behavior of sense data.
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A second broadly epistemological objection claims that the sense data theorist cannot account for our having the concept of physical objects, or for our ability to conceive of the properties of physical objects. This is because, according to the sense data theory, physical objects in principle cannot be directly observed in the way sense data can. Thus, while a sense datum may, for example, be red and round, all physical objects are invisible they cannot be seen.
It makes no sense to say that a color resembles something that is invisible, and similar arguments could be made for all other observable properties besides color; therefore, physical objects cannot in principle resemble sense data. Since we are supposedly never directly aware of physical objects or their properties, and they cannot resemble the things we are directly aware of, it is argued that we could have no conception of the nature of physical objects Berkeley , sections 8—10; Searle , pp.
Sense data theorists are not committed to claiming that sense data look like physical objects. They are, however, committed to claiming that sense data have at least some of the properties that physical objects typically have. In particular, most sense data theorists will agree that physical objects, like sense data, have shapes, though they will typically deny that physical objects have colors or other secondary qualities Locke , II.
Pace Berkeley, it is not unintelligible to speak of an object one is directly aware of having the same shape as an object one cannot be directly aware of. No one thinks, for example, that because an individual H 2 O molecule cannot be seen, it is therefore unintelligible to speak of the molecule's shape. A third epistemological objection derives from Wilfrid Sellars , who questions the traditional account of foundational empirical knowledge knowledge that comes immediately from experience. The epistemological view traditionally taken by sense data theorists has been roughly along these lines Russell The first epistemological objection discussed above questions step d.
Sellars, however, questions step c. He poses a dilemma for sense data theorists: If the awareness is propositional, says Sellars, then it requires the application of concepts. For instance, to be aware that a sense datum is red, one must first have the concept of redness. This is problematic, because it is generally thought that perceptual awareness ought to precede and be independent of concepts.
On the other hand, if the awareness in step b is non-propositional, then it cannot give one the knowledge posited in step c , because that knowledge is propositional — it involves the knowledge that one's sense datum is of a certain kind — and a non-propositional state cannot support a proposition Sellars , part I.
One reply on behalf of the sense data theorist is to note that Sellars' dilemma is not particularly directed at the sense data theory, despite that Sellars formulates it in those terms. That is, if Sellars' argument is compelling, a version of it would apply equally well to direct realist, idealist, or adverbial theories of perception. Sellars' real objection is to the idea of any form of direct awareness providing us with knowledge, whether it be awareness of sense data, physical objects, states of being appeared to, or anything else.
Sellars' intended solution to the problem seems to lie in the direction of a coherence theory of justification. But it is unclear why a sense data theorist could not equally appeal to considerations of coherence, despite that historically all or most sense data theorists have in fact been foundationalists.
A second reply, on behalf of the sense data foundationalist, is that Sellars has confused propositional awareness with conceptual awareness. One might enjoy an immediate awareness of a sense datum as having a certain specific shade of color for which one has no preexisting concept. The awareness would thus be non-conceptual but propositional: If sense data have the properties that perceptually appear to us, then among other things, visual sense data have sizes and shapes. If so, then they occupy space. It is therefore fair to ask where in space they are located.
But there does not seem to be any plausible answer to this Huemer , pp. A further objection to both answers 2 and 3 is that they conflict with the special theory of relativity, since in some cases, they would require one's brain state to cause a sense datum to appear outside one's forward light cone, and the theory of relativity precludes causal relations with events so situated.
As we have noted, sense data are supposed to have precisely the properties that are presented to us in perceptual experience. If one has an experience of seeming to see something red, then one's sense datum is red; equally importantly, if one is not having an experience of seeming to see something red, then one does not have a red sense datum.
A problem with this is raised by the observation that it is sometimes indeterminate what properties objects appear to us to have. To say that it is indeterminate what properties an object appears to have is to say that the object appears to instantiate some determinable , but there is no specific determinate falling under that determinable that it appears to instantiate.
For example, an object might appear to fall within a certain range of colors, while there is no exact shade of color that it appears to have. Chisholm discusses a case in which one sees a speckled hen for a moment, but one is unable to say how many speckles one saw. Other, perhaps more convincing pieces of evidence for indeterminate appearances include our inability to say exactly how far away certain objects seem to be, our inability in some cases to say merely on the basis of appearances whether two objects are the same color, and our inability to read blurred or far-away words.
Hardin discusses psychological experiments that seem to demonstrate indeterminacy of color and shape appearances: If the apparent properties of objects of perception are sometimes indeterminate, then the sense data involved would have to be metaphysically indeterminate — that is, they would have to actually lack definite characteristics.
This, however, is logically impossible — an object cannot be speckled but have no particular number of spots; an object cannot be colored but have no particular shade of color; and so on. This sort of problem only arises when, as sense data theorists do, one analyzes appearance in such a way that there must always be an actual object that has all and only the properties that appear to the subject Huemer , pp.
A related problem is raised by cases of inconsistent appearances, as in the case of the waterfall illusion. This is an illusion in which objects appear, at each moment during an extended time interval, to be moving, yet they never change their positions in the visual field.
The sense data theory would seem to demand sense data with inconsistent properties in such a case Hardin , p. Sense data theorists may respond to these problems by denying, pace Ayer, that sense data have exactly the properties they appear to have. Ayer, Alfred Jules color dualism Hume, David intentionality knowledge: What Are Sense Data? The Standard Conception 1. Arguments for Sense Data 2. The Argument from Perspectival Variation 2. The Argument from Illusion 2. The Argument from Fallibility 2.
The Argument from Hallucination 2. The Argument from Double Vision 2. The Time Gap Argument 2.