Title: Justifying Deductive Reasoning
时间：2017年5月26日下午2:00-4:00
地点：北京大学二教底层北大创新创业中心

讲演人简介
Ahti Pietarinen is Professor of Philosophy and Research Director of Peirce Research Centre at the University of Helsinki, Finland, and Tallinn University of Technology, Estonia. He works on semiotics, pragmatism, and philosophy of language and logic. Author of Signs of Logic: Philosophy of Language, Games and Communication, he is currently preparing a book Logic of the Future on Peirce’s writings on pragmaticism and the graphical approach to logic.  
Justifying Deductive Reasoning
Why does one truth follow from another? Since everything does not follow, there must be some reason for this. The problem of the justification of logical consequence relation has been taken as problematic, since if this reason states a truth not already stated in the premises, then the conclusion did not really follow from the original premises that were stated without this reason. On the other hand, if the reason does not involve such a truth, it does not answer the question. If there is any reason why a conclusion follows logically from premises, there must be a reason why it follows from those premises with that reason as well as without it, and there must be a reason for this, too, and so on ad infinitum. This talk presents Peirce’s solution to the justification of reasoning, which is based on two pillars of his philosophy of logic: (i) The un-eliminability of leading principles of reasoning, which are taken as habits of reasoning, and (ii) the observational nature of deductive reasoning. From the analysis of these pillars we see that the laws of logic arise from the inherently diagrammatic nature of residuation (Peirce’s Rule). As residuation involves observational elements, justification of logical laws is not burdened by circularity or paradox. The same point concerning the observational element that justifies deductive reasoning also holds for adjunctions.  
主持人：陈波教授