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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