The continuity between formal and informal methods of demonstration in philosophical practice

Abstract

The role of logic in philosophy is fundamentally methodological since it is through the usage of different demonstrative structures that philosophical theses are established. Given the variety of modes of presentation of philo-sophical texts, I understand that for the thesis of the methodological role of logic in philosophy - in an encompassing sense - to be defended, logic has to be taken in its most general conception, involving both formal and informal logic. I argue that, even considering the various forms of philosophical de-monstration and the various possible relationships between logic and philo-sophy, there is a continuity between formal and informal methods of de-monstration. In order to show this continuity, I will start from the fundamen-tal notion of logical inference to establish criteria for distinguishing between the formal and the informal, and I will briefly reconstruct the philosophical history of logic to show its transformations and its progressive distancing of its methodological role in philosophy. Finally, considering the recent literatu-re on formal and informal logic, I will point out problems with respect to their differences and, from the recognition that logic plays a methodological role in philosophy, I will argue that formal and informal logic are practices that are in continuity and are mutually beneficial. With respect to the way in which informal logic benefits from formal logic, the article will investigate the advantages and the limitations in taking systems of natural deduction as instruments of analysis of demonstrations in natural language. With respect to how formal logic benefits from informal logic, I will show that advances in formal logic depend upon not only efforts for formalising informal proofs, but also from an informal analysis of calculi strategies and from the princi-ples according to which a logical language operates.