Quantified Temporal Alethic Boulesic Doxastic Logic

The paper develops a set of quantified temporal alethic boulesic doxastic systems. Every system in this set consists of five parts: a ‘quantified’ part, a temporal part, a modal (alethic) part, a boulesic part and a doxastic part. There are no systems in the literature that combine all of these branches of logic. Hence, all systems in this paper are new. Every system is defined both semantically and proof-theoretically. The semantic apparatus consists of a kind of $$T \times W$$ T × W models, and the proof-theoretical apparatus of semantic tableaux. The ‘quantified part’ of the systems includes relational predicates and the identity symbol. The quantifiers are, in effect, a kind of possibilist quantifiers that vary over every object in the domain. The tableaux rules are classical. The alethic part contains two types of modal operators for absolute and historical necessity and possibility. According to ‘boulesic logic’ (the logic of the will), ‘willing’ (‘consenting’, ‘rejecting’, ‘indifference’ and ‘non-indifference’) is a kind of modal operator. Doxastic logic is the logic of beliefs; it treats ‘believing’ (and ‘conceiving’) as a kind of modal operator. I will explore some possible relationships between these different parts, and investigate some principles that include more than one type of logical expression. I will show that every tableau system in the paper is sound and complete with respect to its semantics. Finally, I consider an example of a valid argument and an example of an invalid sentence. I show how one can use semantic tableaux to establish validity and invalidity and read off countermodels. These examples illustrate the philosophical usefulness of the systems that are introduced in this paper.

The Moral Law and The Good in Temporal Modal Logic with Propositional Quantifiers

The Moral Law is fulfilled (in a possible world w at a time t) iff (if and only if) everything that ought to be the case is the case (in w at t), and The Good (or The Highest Possible Good) is realised in a possible world w' at a time t' iff w' is deontically accessible from w at t. In this paper, I will introduce a set of temporal alethic deontic systems with propositional quantifiers that can be used to prove some interesting theorems about The Moral Law and The Good. First, I will describe a set of systems without any propositional quantifiers. Then, I will show how these systems can be extended by a couple of propositional quantifiers. I will use a kind of TxW semantics to describe the systems semantically and semantic tableaux to describe them syntactically. Every system will include a constant · that stands for The Good. ‘·’ is read as ‘The Good is realised’. All systems that contain the propositional quantifiers will also include a constant '*' that stands for The Moral Law. '*' is read as ‘The Moral Law is fulfilled’. I will prove that all systems (without the propositional quantifiers) are sound and complete with respect to their semantics and that all systems (including the extended systems) are sound with respect to their semantics. It is left as an open question whether or not the extended systems are complete.

INSTANTIAL NEIGHBOURHOOD LOGIC

This paper explores a new language of neighbourhood structures where existential information can be given about what kind of worlds occur in a neighbourhood of a current world. The resulting system of ‘instantial neighbourhood logic’ INL has a nontrivial mix of features from relational semantics and from neighbourhood semantics. We explore some basic model-theoretic behavior, including a matching notion of bisimulation, and give a complete axiom system for which we prove completeness by a new normal form technique. In addition, we relate INL to other modal logics by means of translations, and determine its precise SAT complexity. Finally, we discuss proof-theoretic fine-structure of INL in terms of semantic tableaux and some expressive fine-structure in terms of fragments, while discussing concrete illustrations of the instantial neighborhood language in topological spaces, in games with powers for players construed in a new way, as well as in dynamic logics of acquiring or deleting evidence. We conclude with some coalgebraic perspectives on what is achieved in this paper. Many of these final themes suggest follow-up work of independent interest.

End extensions of models of weak arithmetics

Η διδακτορική διατριβή ασχολείται με τη μελέτη προβλημάτων που αφορούν τελικές επεκτάσεις μοντέλων υποσυστημάτων της πρωτοβάθμιας αριθμητικής Peano. Πιο συγκεκριμένα, το πρόβλημα του J. Paris: «Υπάρχει, για κάθε αριθμήσιμο μοντέλο της Σ_1 συλλογής γνήσια τελική επέκτασή του που ικανοποιεί την ∆_0 επαγωγή;» παραμένει ανοικτό.Το πρόβλημα μελέτησαν οι J. Paris και A. Wilkie (1989), οι οποίοι απέδειξαν ότι ικανή συνθήκη για θετική απάντηση είναι το μοντέλο να είναι I∆_0 -πλήρες (όπου με I∆_0 συμβολίζεται η θεωρία της ∆_0 -επαγωγής). Αποδεικνύουμε ότι η χρήση της έννοιας της I∆_0 -πληρότητας μπορεί να παρακαμφθεί και στη θέση της να χρησιμοποιηθεί η τυποποίηση του κλασικού επιχειρήματος του θεωρήματος πληρότητας (θεώρημα Hilbert-Bernays), με χρήση σημασιολογικών πινάκων (semantic tableaux).Επιπλέον, με την ίδια μεθοδολογία κατάλληλα τροποποιημένη αποδεικνύουμε τη γενίκευση του αποτελέσματος, δηλαδή ότι για κάθε αριθμήσιμο μοντέλο της Σ_n -συλλογής, n > 1, υπάρχει γνήσια Σ_n -στοιχειώδης τελική επέκτασή του που ικανοποιεί την ∆_0 -επαγωγή.