The project explores a view of the mind according to which it is fragmented. With belief as the exemplary mental state, the working hypothesis of fragmentation includes four claims:
- The total belief set of a single person’s mind is fragmented into separate belief systems.
- Each belief system is consistent and, we propose, a multiple-premise deductive closure principle holds for obvious consequences within each system.
- The belief systems of a single agent work somewhat independently: they may not be consistent with each other and the agent may not believe the consequences of his belief fragments taken together.
- Different belief systems of a single agent guide the agent’s actions in different contexts.
Although something like Fragmentation can be found in the work of Cherniak, Egan, Elga, Lewis, Rayo, and Stalnaker, few today endorse Fragmentation. The orthodox, often implicit, view – underlying formal and non-formal inquiries – is that the mind is unified:
Agents have a unified representation of the world, a single system of beliefs, organized by two principles:
- Consistency: The total set of an agent’s beliefs is consistent.
- Closure: The total set of an agent’s beliefs is deductively closed. That is, agents believe the deductive consequences of their beliefs.
In the literature, Unity is sometimes endorsed with significant qualifications. It is often endorsed not as a descriptive claim about what finite cognitive agents are like but as a normative claim about what a rational overall belief state is like. Nevertheless, it is endorsed.
Despite widespread reliance on Unity, its picture of the mind faces serious challenges. We focus on a number of problems – some for the descriptive and some for the normative version of Unity – where the fragmentation view promises to offer a superior alternative.
A) It is patently obvious that as a descriptive claim, Unity is a gross mischaracterization of people’s beliefs and of related cognitive abilities. Human agents constantly fall short of keeping their beliefs consistent and drawing all the logical consequences from their beliefs. Take for instance the following three categories of cases that illustrate common failures of Consistency and Closure:
- Ordinary cases of inconsistent beliefs. Paul believes that China is the world’s second-largest national economy. Paul also believes that China is not a member of the G8. Yet Paul believes that the G8 consists of the governments of the eight largest economies in the world.
- Cases of failure to “put the pieces together.” Eva believes that everyone with a yearly income above 40.000 Euros should give 10% of their income to charity. Eva also believes that she earns 50.000 Euros a year. But she fails to believe that she should give 10% of her income to charity.
- Cases of cognitive dissonance. Anna, a feminist academic, asserts sincerely and with conviction that men and women are equally competent in all scientific fields. Nevertheless, she is systematically sexist in most of her automatic behaviour, unreflective judgments and subjective experiences. Anna is aware of her biases and tries to control them, but she is unable to eliminate them.
Cases of type (1) and (3) exhibit violations of Consistency, cases of type (2) exhibit violations of Closure. One goal of the project is to explore whether a single view of fragmentation can explain human belief and agency in all such cases. For illustration, the bare outline of the explanation of inconsistent beliefs looks like this: Inconsistent beliefs belong to distinct fragments of belief, which are accessed, and guide action, under different circumstances or for different purposes, so that the inconsistency is not noticed. Similarly for cases of Closure failure: an agent may hold the belief that P in one fragment, and the belief that if P then Q in another, so that in neither fragment it deductively follows that Q. Thus the agent may fail to draw the conclusion that Q.
B) As normative claims about the rationality of belief (and other attitudes), Unity’s assumptions of Consistency and Closure also face major difficulties. Here are three of the most prominent ones:
- The Problem of Deduction. Real-life agents are not in general consistent and do not draw all the deductive inferences from their beliefs. This is known as the problem of deduction for many theories of belief content and standard epistemic and doxastic logics that adopt Unity as a simplifying or idealizing assumption. Importantly, the problem also has a normative dimension: It is far from clear that ideally rational human agents with finite cognitive capacity should have a single coherent and deductively closed corpus of beliefs.
- Preface Paradox. It is rational for a book author to believe all the statements she makes in the book. At the same time, it is rational for her to admit her fallibility, i.e. to admit that at least one of these beliefs is false. Thus, it is rational for her to have inconsistent beliefs: a set of beliefs and the belief that at least one of them is false. This paradox provides reason to reject Consistency (and Closure): it can be ideally rational to hold inconsistent beliefs. Since we should admit our fallibility regarding almost any subject matter, having inconsistent beliefs seems to be a fundamental feature of rationality.
- Frege’s puzzle. Marie rationally believes that Hesperus is the brightest object in the evening sky. Marie also rationally believes that Phosphorus is not the brightest object in the evening sky. Since Hesperus is Phosphorus, Marie holds inconsistent beliefs – at least on a very popular view about belief content. Thus Marie would count as irrational. However, Marie seems fully rational in her beliefs; she just lacks the knowledge that Hesperus is Phosphorus. We surmise that it is Unity – the assumption of a single, unified and consistent set of beliefs – that gives rise to Frege’s puzzle, and that the puzzle can be solved on a fragmentation view of the mind.