Nicolien Janssens

From different angles of science, there has been a growing interest in the abilities of groups to track the truth. The Condorcet Jury Theorem (1785) states that without communication, infinitely big groups will reach a correct majority opinion with certainty. Coughlan (2000), meanwhile formulated a model in which all agents communicate with each other, showing that majorities are only just as good as fully-communicating individuals. In reality, communication is usually between these two extremes: some agents communicate with some of the others, but not with all others. We refer to this as partial communication. This thesis provides a Bayesian framework to study the influence of partial communication on individual as well as group accuracy, thereby generalising Condorcet’s as well as Coughlan’s setting. We obtain results for individual and group accuracy in three type of networks. Firstly, we study the extreme case where there is either no communication or everyone communicates with everyone. Secondly, we determine accuracy for regular networks, in which all agents communicate with equally many other agents. Thirdly, we derive a formula to express the expected accuracy in random networks, in which agents can communicate with various numbers of other agents. The formula enables us to determine the effect of various parameters on the individual and group accuracy in a random network with partial communication. Finally, we show that in random networks, despite correlation between agents, we can still obtain accurate majorities under some constraints.

Based on the brain in a vat thought experiment, skeptics argue that we cannot have certain knowledge. At the same time, we do have the intuition that we know some things with certainty. A way to justify this intuition is given by semantic contextualists who argue that the word “knows” is context sensitive. However, many have objected to the intelligibility of this claim. In response, another approach called “moderate pragmatic contextualism” was invoked, which claims that “knows” itself is not context sensitive, but knowledge assertions are. I show, however, that to refute skepticism, moderate pragmatic contextualism rests on unjustified and implausible assumptions as well. Since no form of contextualism works as a response to skepticism, I argue that we should simply accept skepticism. However, I argue that skepticism is not a problem because skeptic pragmatic contextualism can offer a plausible explanation of why we have the intuition that our ordinary knowledge claims are true, even though they are not. I conclude that skeptic pragmatic contextualism offers the most plausible response to the brain in a vat thought experiment.

Based on the brain in a vat thought experiment, skeptics argue that we cannot have certain knowledge. At the same time, we do have the intuition that we know some things with certainty. A way to justify this intuition is given by semantic contextualists who argue that the word “knows” is context sensitive. However, many have objected to the intelligibility of this claim. In response, another approach called “moderate pragmatic contextualism” was invoked, which claims that “knows” itself is not context sensitive, but knowledge assertions are. I show, however, that to refute skepticism, moderate pragmatic contextualism rests on unjustified and implausible assumptions as well. Since no form of contextualism works as a response to skepticism, I argue that we should simply accept skepticism. However, I argue that skepticism is not a problem because skeptic pragmatic contextualism can offer a plausible explanation of why we have the intuition that our ordinary knowledge claims are true, even though they are not. I conclude that skeptic pragmatic contextualism offers the most plausible response to the brain in a vat thought experiment.

The rigid designation of proper names and natural kind terms is the most well-known doctrine of Kripke’s Naming and Necessity (1981). On the basis of rigidity, Kripke has shown that proper names and natural kind terms do not refer via a description as argued by descriptivists. In response to Kripke several people have argued that all general terms could be interpreted rigidly, which would make the notion of rigidity trivial. This leads to the ‘rigidity problem’: the notion of rigidity cannot be used to argue against descriptivism anymore. I will show that the rigidity problem appears on a larger scale: firstly, because it appears independently of the trivialisation problem, secondly, because it appears for descriptions acting like singular terms as well. I will argue, however, that proper names and natural kind terms differ in an important manner from rigid descriptions. While the first are de jure rigid, the latter are de facto rigid. I will show that the rigidity problem indeed appears for de facto rigidity, but not for de jure rigidity, with the result that Kripke’s argument against descriptivism can withstand.