Abstract
Like belief revision, conceptual change has rational aspects. The paper discusses this for predicate change. We determine the meaning of predicates by a set of imaginable instances, i.e., conceptually consistent entities that fall under the predicate. Predicate change is then an alteration of which possible entities are instances of a concept. The recent exclusion of Pluto from the category of planets is an example of such a predicate change. In order to discuss predicate change, we define a monadic predicate logic with three different kinds of lawful belief: analytic laws, which hold for all possible instances; doxastic laws, which hold for the most plausible instances; and typicality laws, which hold for typical instances. We introduce predicate changing operations that alter the analytic laws of the language and show that the expressive power is not affected by the predicate change. One can translate the new laws into old laws and vice versa. Moreover, we discuss rational restrictions of predicate change. These limit its possible influence on doxastic and typicality laws. Based on the results, we argue that predicate change can be quite conservative and sometimes even hardly recognisable.
Highlights
Though the operations affect the analytic laws of the language, we show that the model change entails no incommensurablity: one can translate statements from the old to the new system
We discuss predicate changes with respect to other laws by raising two questions: First, how can doxastic or typicality laws motivate a conceptual change? Second, how can predicate change be evaluated with respect to the consequences it has for these other laws? The final conclusion gives a sketch of how our results can be applied to two central subjects of philosophy, namely the understanding of conceptual change and the role of analytic laws
We introduced typicality laws that allow for real exceptions, for example, “Birds can fly”
Summary
The core idea of PAL is to model the effects of the public announcement of a statement P on the knowledge of (groups of) agents. This is realised by a model change, namely a reduction of the epistemic possibilities to worlds that comply with the announced P. The distinction between heat and temperature, the rising of the concept of mass, or the introduction of complex numbers give a new structure of epistemic possibilities Such severe changes, dubbed “conceptual revolution” by [30], are often associated with different thought styles or incommensurability (cf [12, 16]). We discuss predicate changes with respect to other laws by raising two questions: First, how can doxastic or typicality laws motivate a conceptual change? Second, how can predicate change be evaluated with respect to the consequences it has for these other laws? The final conclusion gives a sketch of how our results can be applied to two central subjects of philosophy, namely the understanding of conceptual change and the role of analytic laws
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