Carlo Proietti

Group polarization occurs when an initial attitude or belief of individuals becomes more radical after group discussion. Polarization often leads subgroups towards opposite directions. Since the 1960s this effect has been observed and repeatedly confirmed in lab experiments by social psychologists. Persuasive Arguments Theory (PAT) emerged as the most convincing explanation for this phenomenon. This paper is a first attempt to frame the PAT explanation more formally by means of Bipolar Argumentation Frameworks (BAFs). In particular, I show that polarization may emerge in a BAF by simple and rational belief updates by participants.

The history of reasoning about time is disseminated with paradoxes and conundra and contemporary physics does not make an exception. Logics in general, and more in particular temporal logics, represent a rigorous formal tool in order to solve or clarify problems of this kind. In what follows we will first explain, from the point of view of philosophical logic, what is a paradox and what should count as a solution for it. After that we will illustrate A.N. Prior's formalization of the traditional paradox of future contingency and determinism. Then we will focus on two modern paradoxes – the twin paradox and the time travel paradox – and show how an adequate temporal logic can help their framing and understanding.

The Peter Principle states that employees tend to be promoted until they reach their level of incompetence. In a sophisticated simulation study, Pluchino et al (2010) confirmed a version of the principle. However, they also noted that their model has the counterintuitive consequence that "the best ways for improving the efficiency of a given organization are either to promote each time an agent at random or to promote randomly the best and the worst members". We argue that what promotion rule is used can in general influence employee productivity (which is here seen as part of competence). Accommodating this psychological aspect of promotion is noted as an open problem by Pluchino et al. Using an amended simulation model we verify that if the incentive induced by promoting the best is strong enough, then that strategy will be optimal. In a final simulation experiment we consider the effect on the efficiency of an organization of using "double standard" promotion ...

The philosophical inquiry of Arthur Prior (1914-1969) has involved topics ranging from formal logics to ethics, while giving crucial contributions in modal logic, metaphysics, and the philosophy of time. Prior is considered the father of temporal logic and a forerunner of both current hybrid logic and Kripke's possible worlds semantics; also, he has supported a refined and go-ahed version of actualism, that in turn he grounds on a specific view on the relation between existence, facts and truths. Prior's approach to philosophy has been highly sensitive to the traditional big questions in metaphysics and ontology, and at the same time has laid the grounds of new areas of research in modal logic. The present entry aims at presenting and discussing some of Prior's most important contributions to philosophy and their relevance. In particular, the entry presents and discuss branching-time semantics and their application to the problem of determinism, hybrid logics and the red...

This paper presents two systems of temporal logic, ΛCPT and ΛCPT@, with ceteris paribus modalities. The principal aim is to show how this approach can be useful to give an ockhamist solution to the future contingents problem along the same lines of A. Prior in Prior (1967). The interest of this work lies also in the fact that ΛCPT@ represents an alternative modal account of supervaluationist and post-semantics approaches to temporal reasoning

A group is in a state of pluralistic ignorance (PI) if, roughly speak-ing, every member of the group thinks that his or her belief or desire is different from the beliefs or desires of the other members of the group. PI has been invoked to explain many otherwise puzzling phenomena in social psychology. The main purpose of this article is to shed light on the nature of PI states -their structure, internal consistency and opacity -using the formal apparatus of Dynamic Doxastic Logic, and also to study the sense in which such states are "fragile", i.e. to iden-tify plausible conditions under which a PI state cascades into a state of shared belief as the result of announcement.

La Sintassi logica del linguaggio [1] rappresentava tra altre cose, nelle inten-zioni di Carnap, una spiegazione ed una giustificazione, alla luce degli allora recenti risultati di Gödel, di un punto di vista convenzionalista riguardo ai fondamenti della matematica e del discorso scientifico in generale. L'im-magine di convenzionalismo che ne risultà e molto complessa e, per diversi aspetti, di difficile interpretazione. Una prima parte di questo lavorosa a dedicata all'elucidazione del pro-blema dei fondamenti per come si presentava a Carnap al momento della stesura del suo lavoro, nonché all'analisi delle posizioni filosofiche che de-terminano il contenuto della Sintassi e,pì u determinatamente, la scelta dell'opzione metalinguistica. Il metalinguaggio rappresenta infatti, nella vi-sione di Carnap, il corretto metodo della filosofia della scienza e,pì u in particolare, dell'analisi del problema dei fondamenti. Una seconda sezione sa a dedicata ad enucleare i motivi per cui l'atteggiamento convenzionalista si adatta al punto di vista di un empirista, quale era Carnap, nello spiegare la nozione dianalitici a onecessi a logico-matematica 1 . Le basi e le ragioni della spiegazione di tale concetto da parte di un logico neo-empirista sono chiaramente molto diverse da quelle che avrebbe fornito un empirista tra-dizionale. L'ultima sezione mette a confronto la posizione di Carnap, per come sì e venuta delineando, con la "refutazione", da parte di Gödel, del punto di vista fondazionale espresso dalla Sintassi e del convenzionalismo in generale. La refutazionè e argomentata da Gödel proprio sulla base del significato filosofico dei suoi due celebri risultati metamatematici 2 , e e pro-prio sul terreno del metalinguaggio che si gioca il confronto possibile tra le motivazioni dei due. 1 I due termini saranno, nel seguito, usati alternativamente come sinonimi. 2 Le critiche di Gödel sono svolte all'interno di alcuni saggi ([8] e [7]) rimasti non pubblicati fino all'edizione del terzo volume delle Opere Complete di Gödel, avvenuta nel 1995. La pubblicazione di questi saggi ha dato nuovo impulso alla discussione di questo aspetto problematico del convenzionalismo carnapiano (ad esempio, l'intera terza parte di Reconsidering logical Positivism di M. Friedman [6 e dedicata alla nozione carnapiana di "Veri a logico-matematica" e, in buona parte, alle obiezioni di Gödel).

The present work is motivated by two questions. (1) What should an intuitionistic epistemic logic look like? (2) How should one interpret the knowledge operator in a Kripke-model for it? In what follows we outline an answer to (2) and give a model-theoretic definition of the operator K. This will shed some light also on (1), since it turns out that K, defined as we do, fulfills the properties of a necessity operator for a normal modal logic. The interest of our construction also lies in a better insight into the intuitionistic solution to Fitch’s paradox, which is discussed in the third section. In particular we examine, in the light of our definition, DeVidi and Solomon’s proposal of formulating the verification thesis as \(\phi \rightarrow \neg \neg K\phi\) . We show, as our main result, that this definition excapes the paradox, though it is validated only under restrictive conditions on the models.

The paper attempts to give a solution to the Fitch’s paradox though the strategy of the reformulation of the paradox in temporal logic, and a notion of knowledge which is a kind of ceteris paribus modality. An analogous solution has been offered in a different context to solve the problem of metaphysical determinism.