Hume’s argument for skepticism in Enquiry

In the Enquiry, Hume begins with the statement that human beings have no innate knowledge and that all ideas are born from sensory impressions. Once we have these ideas in our mind, we are, in some cases, free to explore them without constant access to the sense perception, but only after we have first had an experience of whatever idea it is that we are exploring. After establishing this, he goes on to pose two categories which our thoughts can be divided into. The first of these categories he calls the “Relations of Ideas.” This category includes those few things which Hume believes we are able to have certain knowledge of. These things are primarily Mathematics, Geometry, and Logic. Hume believes that these things, though they must first be experienced through the senses are thereafter available to our minds in the same way that I, having seen a triangle, do not need to have a triangle in front of me in order to know what constitutes a triangle. The second category that Hume posits is known as the Matters of Fact. This category contains basically everything that is not, mathematic, geometric, or logical. The things which make up this category are totally dependent on the senses in the same way that, even after I have first experienced the color blue, I am unable to give a definition of blue other than to point to a sensory perception and say “That object is blue.” Next, he deals with the ways in which human beings organize these matters of fact. Hume states that we link the matters of fact together in our thought in three primary ways. The first of these ways is Resemblance. That is to say, that we group ideas together according the resemblance they bear toward one another, in the way that ice cubes resemble snow in being cold and frozen. Secondly, we group ideas according to Contiguity. This is to say that we group things in time and space according to when and where we sense them. Finally, we place ideas in causal relations by saying that event “A” causes event “B.” According to Hume, not only are these matters of fact completely dependent upon our sensory perceptions, but they are also wholly unable to be judged as existent or true in any way. This is, Hume states, because we have no way of sensing any force of causality. Therefore, we have no way of knowing if the linkages we draw between matters of fact exist, and we also have no way of knowing if there is any reality behind our sensations beyond pure sense perception. Also, because we have no understanding of causality and indeed no certainty in the existence of the world itself, we then are also completely unable to place our certain trust in the sciences. Lastly, because we have no sensation of causality, we have no way of knowing that the future will resemble the past, which means we can only act upon probabilities, rather than upon the belief that something will happen because it has happened in the same way before. Because we have no way of knowing of the existence of causality, or any like between future and past, we have no way of knowing what, if anything, causes our impressions of the world. Lastly, according to Hume, because all human ideas must be grounded in sense data, anything which is spoken of by a human being, but which cannot be experienced as an impression, is nothing more than a mixing of formerly sensed impressions, is worthless, and must be thrown out. Having made these statements, Hume leaves us with an unbridgeable epistemological gap between the self and the outside world, and no true and certain knowledge may be gleaned about the world beyond that gap. Kant, however, believes he has found an answer to Hume’s skepticism and, in the Prolegomena, he attempts to lay out the bridge across this epistemological gap. This is an undertaking that he is only partially successful in accomplishing.

Prolegomena to Any Future Metaphysics

 Analytic and Synthetic Judgements

First in the Prolegomena, Kant redefines Hume’s categories of ideas. This first category he names Analytic Judgments. These analytic judgments, Kant believes, are apriori in nature. By this, he means that they exist independent of the physical world, are intuitive, and are not derived from the physical world. Also, they can be known to be certain, and generally explain through process of definition and logic. I believe Hume’s example of “Bachelor” being defined as an unmarried man, would fit into this category. Likewise, this category corresponds roughly with Hume’s Relations of Ideas. The second category which Kant divides human ideas into corresponds roughly with Hume’s Matters of Fact. Kant names this category Synthetic Judgment, or Synthetic Aposteriori Judgment. The Synthetic Judgments are those judgments which are made through the use of the senses about the world around us. These Synthetic Judgments, Kant states, are not able to be known with certainty, and are dependent on the physical reality. An example of this category would be a statement along these lines. “This book bag is blue.” The truth of this statement is reliant on whether the book bag truly is blue or not and relies upon sensation for its confirmation. Though both of these categories are useful, Analytic judgments being useful in that they can be certain and synthetic judgments being useful in that they are applicable to the world, only these two categories would not be sufficient to allow Kant to escape from the skepticism which Hume found himself in. Therefore, Kant recognizes the need for a third category of ideas which are able to bridge the gap between the self and the external world with the certainty of judgments intact.

Synthetic a priori knowledge

Kant labels this third category Synthetic a priori Knowledge, and states that the things which fall under this category are both intuitive (a priori), and constant, but also must be applied to the world to form synthetic judgments which vary with changing sensation. Included in this category are The Forms of Sensibility, and the Categories of the Understanding. These two concepts are what Kant believes have enabled him to escape the skepticism of Hume. So, to fully understand Kant’s argument, we must explore the nature of these concepts. In setting out his thoughts, Kant began to study the world and came across a few simple truths about the way in which every human being experiences the world. These truths are as follows. Every human being experiences the world in both space and time. This is to say, that any object which is experienced by a human is experienced as existing somewhere in the space that is around them, and is also experienced as existing in time, be it the present time, as something they are currently examining, the past, as a memory of what once was, or the future, as an idea of something that will come to pass. Also in studying human sense perceptions, Kant comes to believe that there are only twelve types of judgments that can be made by a human being about the world. That is to say, that every judgment made by a human being about anything that exists to him or her physically will fit invariably into one of these twelve categories. These discoveries on Kant’s part form the basis for his theories of the Forms of Sensibility, which are space and time, and also the Categories of Understanding, which explain the way in which human beings process their experiences of the world. These forms and categories must have sense data with which to interact. Because of this, Kant posits the existence of the Noumenal World.

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Skepticism and logical possibility

While skepticism takes many different forms, the primary form of skepticism under consideration can be described by single, general argument. This skepticism’s basic premise is that we are unable to logically disprove possible states of affairs in the world that would undermine our claims to knowledge about reality (“skeptical possibilities”). Generally, arguments for skepticism, including the original Cartesian skepticism formulation, ultimately take the form of a modus ponens argument, such as,

1. If I can not distinguish between dreaming and being awake, then I can not be sure I have a body.
2. I can not distinguish between dreaming and being awake.
3. Therefore, I can not be sure that I have a body.

Support for the second premise derives from the possibility that, for any empirical proposition we form at a point in time, events could follow that would provide evidence to falsify that belief. If this is true, no empirical proposition is verifiable and thus none are certain.

Wittgenstein does not disagree with this, to an extent; he grants that such subsequent falsifying events are indeed always a possibility. For example, one may have very good reasons for believing his old friend is standing in front of him, but it is imaginable for that person to suddenly start behaving as though he was not that old friend after all (613).[1] However, Wittgenstein challenges the notion that such events transpiring would undermine the relevant prior empirical beliefs about the situation. In other words, he argues that such possibilities do not undermine “knowledge,” in the meaningful sense of the word, but merely fail to satisfy the conditions of a notion of logic removed from practitioners of logic (human beings).

Wittgenstein on doubt

In the second paragraph of On Certainty, Wittgenstein elucidates the role of doubt, almost spelling out immediately what will become his objection against skepticism: “from its seeming to me – or to everyone – to be so, it doesn’t follow that it is so. What we can ask is whether it can make sense to doubt it [emphasis added]” (2). Though the skeptics are correct in questioning the assertion of seeming or “common-sense” empirical fact, such doubts fail to (meaningfully) endorse their assertion that all knowledge can be undermined. Hence, Wittgenstein attacks the core of “radical doubt” as non-sensical.

Primarily, the skeptics make the error of conceiving logic as an empirical statement – as something independent of the agent in question – that is subject to the possibility of falsification. The Tractatus, though earlier in Wittgenstein’s philosophical development, is particularly illustrative of this problem with skepticism: “Propositions cannot represent logical form: it is mirrored in them. What finds reflection in language, language cannot represent.”[2] Moreover, we cannot sensibly falsify (or take any other action standing outside of) logic, since we can not describe what a non-logical world would look like.[3] Yet this is precisely what skepticism demands.

Skepticism, by externalizing logic, thus encounters serious error when it casts extreme doubts upon common-sense propositions, which are necessary for establishing language (and hence the use of logic). When someone says, “There are trees,” he is presupposing the existence of objects. This is not to imply an epistemological assertion that there are objects in a specific sense of the word, but it simply reveals the absurdity of saying “objects do not exist.” If one holds that to be true, he runs into the intractable problem of explaining of what it is that one is speaking when one says “there are trees.” Day to day life demonstrates that common-sense propositions must be known in some way, as evidenced by the fact that we say things to others like “move that table over here” or “open the window” (7). In light of this, the nature of being mistaken about a statement like, “I am certain that these are words on this paper” is unclear (17, 24, 32). What it would be like to find out that “here is not a hand” is peculiar and seemingly indescribable by language. This is because the language-games people use, those ingrained deeply in their practices and beliefs, depend on affirming such propositions in order for them to make any sense (to be explained shortly).

Furthermore, as Wittgenstein asserts several times, the notion of doubt presupposes certainty (115 and elsewhere). In order for one to doubt anything, one must first have certainty about what he doubts, be certain that he, in fact, doubts it, and so on. This relates closely to the foundation of (the human expression of) logic in language, as implied in Tractatus. In Philosophical Investigations, Wittgenstein delves into the nature of language games, which later play an important role in On Certainty. Section 7 of Investigations states, “I shall call it the whole, consisting of the language and the actions into which it is woven, the language-game.”

Learning and language

 Wittgenstein explores how a child learns and the relationship between its learning and language in section 6 of the Investigations. A child learns what words mean by ostensive action; for example, one might instruct, “that is a chair; that is a car; that is red; etc.” In all this, however, there is a necessity for an understanding of ostensive definition itself. A child, to learn that “this is called ‘car’,” must first comprehend that names can be assigned to things. Later, in section 31, Wittgenstein uses an example of teaching someone how to play chess. When he points to a piece and says, “this is the king; it can move like this,…” the phrase “this is called the ‘king’” is only a definition if the student knows what a game is, what a piece in a game is, etc.

The point of the exploration of language games is, in short, that understanding requires some background of trust – some kind of sureness. Continuing in On Certainty with the case of the child, Wittgenstein says, “the child learns by believing the adult. Doubt comes after belief” (160). A child could never learn anything if he constantly questioned existence, for if that were to happen, he could never learn the definitions of things ostensively, just as if a person were to question the game or the pieces of chess, he would never learn that “this is called “the king” and it moves like so.”

The process of learning language is one of action (or reaction) first, then epistemological reflection at a later time once a system of beliefs is formed and it becomes gradually understood where doubt can be reasonable (538). For example, a child initially listens to verbal and written instructions, responding trustingly and candidly to what others say. When a child realizes that people have the capability to lie, however, he then has a reasonable basis for sometimes doubting the truth of what someone says. The system of belief he develops is essential to forming these kinds of curiosities and doubts. If he did not understand that other human beings like himself existed and behaved autonomously and with similar capabilities, he could not even begin to comprehend the notion of doubting the truth of their words. Moreover, even when he believed and spoke candidly, he would not have been able to do so had he questioned the existence of other human beings, and he would have not been able to understand the existence of other human beings if he questioned the existence of a world external to him.

Language is inextricably embedded into our lives. Without it, we would be unable to learn, and without learning, we would be unable to doubt. Further, it is the common understanding and foundations of language that allow human beings to communicate. Incidentally, by no means is the plain use of signs universally indicative of meaning (another basic idea explored in Tractatus that blocks a potential route for skepticism). A person who interprets and acts upon the mathematical directive “halve” by multiplying by three hundred is not casting doubt upon halving, but is merely out of sync with the rules and norms of a language-game. He is not presenting a skeptical challenge to knowledge of mathematics.

At the crux of his argument, Wittgenstein rejects the Cartesian-style premise that all propositions, even foundational ones, should be doubted along with any beliefs that they justify, unless they can be proven empirically. The skeptics’ doubt of these propositions does not merely test the truth, falsehood, or likelihood of those propositions, but ultimately necessitates questioning the methods by which testable empirical propositions are tested (317, 318). If all knowledge is based on testable empirical propositions that are justified by methods that are themselves subject to the skeptics’ pervasive doubt, then one must always acknowledge skeptical possibilities (i.e., the skeptics’ position is meaningful).

 Skepticism of the external world isn’t useful

To counter this, Wittgenstein explains that claims like “here is a hand” or “the world has existed for longer than five minutes” merely appear to be statements about the external world that are true or false. However, these propositions lie beyond knowledge or doubt, because they serve as the framework by which we can speak about objects in the world. He uses two metaphors: first, that these kinds of propositions are like a “river-bed” that allow the “river of language” to flow freely (97, 99); and second, that the propositions are like hinges on a door, which must be fixed in order for the door to function in any significant way (341, 343). These kinds of propositions ostensively defined; they are not making an empirical claim about the external world, but merely show an example and hence demonstrate how the statement is to be used. The possibility of language is not made by actual facts in the world (which the skeptic can always undermine), but by simply never calling into question those facts (creating the “river-bed”).[4] Thus, Wittgenstein does superficially agree with the skeptic that such foundational propositions lie beyond empirical verification, but questions the sensibility and usefulness of such an assertion.

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