Abstract

To sentential language we add an operator C to be read as ‘it changes that…’ and present an axiomatic system in the frame of classical logic to catch some meaning of the term ‘change’. A typical axiom is e.g.: CA implies, a basic rule is: from A it may be inferred (theorems do not change). So this system is not regular. On the semantic level we introduce stages (of the development of some world, of some agents’ convictions or of some argumentation) at which a sentence may be true or false. It turns out that with the help of C, an operator N can be defined whose intuitive meaning is ‘on the next occasion…’ and which behaves like A.N. Prior’s F (and also like the T operator of G.H. von Wright’s read ‘… and next…’). In a book by Świetorzecka (2008) cited below, the philosophical background is described which is the Aristotelian theory of substantial change. The author of this book shows also some metalogical properties of this logic. The aim of this text now is to present a formal extraction of Świetorzecka (2008) with a shortened axiomatisation and to describe some metalogical results.