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This paper examines critically the reconstruction of the ‘Sherlock Holmes sense of deduction’ proposed jointly by M.B. Hintikka (1939–1987) and J. Hintikka (1929–2016) in the 1980s, and its successor, the interrogative model of inquiry (imi) developed by J. Hintikka and his collaborators in the 1990s. The Hintikkas’ model explicitly used game theory in order to formalize a naturalistic approach to inquiry, but the imi abandoned both the game-theoretic formalism, and the naturalistic approach. It is argued that the latter better supports the claim that the imi provides a ‘logic of discovery’, and safeguards its empirical adequacy. Technical changes necessary to this interpretation are presented, and examples are discussed, both formal and informal, that are better analyzed when these changes are in place. The informal examples are borrowed from Conan Doyle’s The Case of Silver Blaze, a favorite of M.B. and J. Hintikka.

According to both Jaakko Hintikka and Simo Knuuttila, Aquinas’ third way to demonstrate that God exists presupposes the acceptance of the principle of plenitude, i.e., of the claim that all possibilities are realized at some time. Aquinas, however, maintained elsewhere that not all possibilities are always realized, and the coherence of his philosophical project may be called into question if one were to accept Hintikka’s and Knuuttila’s reading of the third way. In this paper, I argue that it is difficult to present the third way without invoking the principle of plenitude in Hintikka’s formulation. The corollary of this claim is that third way cannot be a demonstration within the philosophical system outlined by Aquinas, despite his claim to the contrary. Against the backdrop of this exegetical discussion, it is possible to rephrase Aquinas’ third way as a probabilistic argument that shows that God’s existence is highly likely, although not necessarily proven.

In a series of papers published in the sixties and seventies, Jaakko Hintikka, drawing upon Kant’s conception, defines an argument to be analytic whenever it does not introduce new individuals into the discussion and argues that there exists a class of arguments in polyadic first-order logic that are to be synthetic according to this sense. His work has been utterly overlooked in the literature. In this paper, I claim that the value of Hintikka’s contribution has been obscured by his formalisation of the original definition. Therefore, I provide (i) a brief reconstruction of the historical framework of the problem and the revolutionary import of Hintikka’s contribution, (ii) a clarification of the most complicated steps of Hintikka’s elaboration of his insight, (iii) a criticism of several features that play a fundamental role in Hintikka’s formalisation and (iv) a selection from Hintikka’s own material of some valuable suggestions towards a clear and workable formalisation. As for the pars construens , I isolate in the approach of depth-bounded first-order logics (D'Agostino et al. 2021) an alternative formalisation of the notion of syntheticity as the introduction of new individuals in the reasoning, and I show that it is not affected by the same difficulties as Hintikka’s proposal. In so doing, I hope to have contributed to the realisation of the project of rehabilitating Kant’s analytic–synthetic distinction in the context of modern first-order logic with the purpose of showing, against the logical empiricist movement, that logic is not analytic.

This is a contribution to the idea that some proofs in first-order logic are synthetic. Syntheticity is understood here in its classical geometrical sense. Starting from Jaakko Hintikka’s original idea and Allen Hazen’s insights, this paper develops a method to define the ‘graphical form’ of formulae in monadic and dyadic fraction of first-order logic. Then a synthetic inferential step in Natural Deduction is defined. A proof is defined as synthetic if it includes at least one synthetic inferential step. Finally, it will be shown that the proposed definition is not sensitive to different ways of driving the same conclusion from the same assumptions.

Abstract The verb ‘to know’ can be used both in ascriptions of propositional knowledge (e.g. ‘Mary knows that Smith smokes’) and ascriptions of knowledge of acquaintance (e.g. ‘Mary knows Smith’). In the formal epistemology literature, the former use of ‘know’ has attracted considerable attention, while the latter is typically (dis)regarded as derivative. This attitude may be unsatisfactory for those philosophers who, like Russell, are not willing to think of knowledge of acquaintance as a subsidiary or dependent kind of knowledge. In this paper we outline a logic of knowledge of acquaintance in which ascriptions like ‘Mary knows Smith’ are regarded as formally interesting in their own right, remaining neutral on their relation to ascriptions of propositional knowledge. The resulting logical framework, which is based on Hintikka’s modal approach to epistemic logic, provides a fresh perspective on various issues and notions at play in the philosophical debate on acquaintance.

In Memoriam: Jaakko Hintikka (I-12-1929 Vantaa - VIII-12-2015 Porvoo)

This paper examines whether Sherlock Holmes’ “Science of Deduction and Analysis,” as reconstructed by Hintikka and Hintikka (in: Eco U, Sebeok TA (eds) The sign of three: Peirce, Dupin, Holmes, Indiana University Press, Bloomington, 1983), exemplifies a logic of discovery. While the Hintikkas claimed it does, their approach remained largely programmatic, and ultimately unsuccessful. Their reconstruction must thus be expanded, in particular to account for the role of memory in inquiry. Pending this expansion, the Hintikkas’ claim is vindicated. However, a tension between the naturalistic aspirations of their model and the formal apparatus they built it on is identified. The paper concludes on suggestions for easing this tension without losing the normative component of the Hintikkas’ epistemological model.

In this paper, we shall give another proof of the faithfulness of Blass translation (for short, B-translation) of the propositional fragment L₁ of Leśniewski's ontology in the modal logic K by means of Hintikka formula. And we extend the result to von Wright-type deontic logics, i.e., ten Smiley-Hanson systems of monadic deontic logic. As a result of observing the proofs we shall give general theorems on the faithfulness of B-translation with respect to normal modal logics complete to certain sets of well-known accessibility relations with a restriction that transitivity and symmetry are not set at the same time. As an application of the theorems, for example, B-translation is faithful for the provability logic PrL (= GL), that is, K + □(□φ ⊃ φ) ⊃ □φ. The faithfulness also holds for normal modal logics, e.g., KD, K4, KD4, KB. We shall conclude this paper with the section of some open problems and conjectures.

Epistemic Friction: An Essay on Knowledge, Truth and Logic is a recent work by the influential American analytical philosopher Gila Sher, professor of philosophy at the University of California, San Diego. Sher, expert in the thought of Tarski and Quine, is also a noted contributor to technical debates in current symbolic logic. However, her work and the book in question -designed as one stepping-stone in the construction of a larger philosophical project - witness to very wide philosophical preoccupations. Sher therefore wishes to situate current research in logic within the broader perspectives of philosophy of mind and epistemology. The philosophical vision she outlines witnesses to the «openness» of the world of analytical philosophy in recent times to revisit and perhaps even radically revise the presuppositions on which it was founded over a century ago in order to pursue more authentically the goals of philosophical research. A good number of Sher's philosophical preoccupations, which are far-reaching in scope, are shared in Bernard Lonergan's philosophical writing. The article then opens up a dialogue and debate between the two philosophies. Among the aims of the article is the intention of making evident how fruitful such a dialogue may prove in light of new perspectives in analytical philosophy. But it also raises questions concerning certain empiricist models which, even when not acknowledged, may in effect manifest an undertow in the unfolding of philosophical arguments. The article, which also draws into the discussion the later work of Jaakko Hintikka, opens with remarks on an intriguing crossing of intellectual paths of Bernard Lonergan and one of the central figures in twentieth-century logic and analytical philosophy, Alonzo Church. This moment in Lonergan's early development is enlightening as regards the wider issues treated in the article which concern epistemology, logic and human historically embedded intentionality. The article is to be published in two parts. «Epistemic Friction: An Essay on Knowledge, Truth and Logic» è un récente lavoro di una filosofa analitica americano, Gila Sher, influente nell'ambiente americano, professoressa di filosofia all'università San Diego, in California. Sher, esperta del pensiero di Tarski e Quine, è anche una nota esponente dei dibattiti tecnici nelPattuale logica simbolica. Ad ogni modo il suo lavoro e il libro in questione - pensato come un passo in avanti nella costruzione di un progetto filosofico più ampio - testimoniano ampie preoccupazioni filosofiche. Sher quindi desidera porre la sua attuale ricerca in una logica all'interno di una prospettiva più ampia di filosofia della mente e di epistemologia. La visione filosofica, ehe la Sher delinea, testimonia l'apertura del mondo della filosofia analitica, in tempi recenti, a rivisitare e forse anche rivedere radicalmente le preoccupazioni su cui fu fondata, più di un secolo fa, al fine di perseguire più autenticamente gli obiettivi della ricerca filosofica. Un buon numéro di preoccupazioni filosofiche della Sher, ehe sono ben lontane dal raggiungere lo scopo, sono condivise negli scritti filosofici di Bernard Lonergan. L'articolo, allora, fa sorgere un dialogo e un dibattito tra i due filosofi. Tra le finalità dell'articolo c'è l'intento di rendere evidente quanto un dialogo fruttuoso, di taie tipo, possa porre in luce nuove prospettive nella filosofia analitica. Inoltre fa sorgere anche questioni concernenti certi modelli empiristici ehe, anche quando non conosciuti, possono in effetti manifestare una risacca nel dispiegarsi degli argomenti filosofici. L'articolo, che porta nella discussione anche l'ultimo lavoro di Jaakko Hintikka, si apre, con considerazioni su un'intrigante connessione di percorsi intellettuali di Bernard Lonergan e di una delle figure centrali nella logica del ventesimo secolo e nella filosofia analitica, Alonzo Church. Questo momento nello sviluppo iniziale di Lonergan è illuminante riguardo a questioni più ampie trattate nell'articolo ehe concernono l'epistemologia, la logica e l'intenzionalità umana, storicamente disegnata. L'articolo viene pubblicato in due parti.

One of the many research projects of Jaakko Hintikka was entitled \"Logical tools for human thinking and their history\". This is in fact an apt summary of the lifetime work of this master logician who developed several new methods and systems in mathematical and philosophical logic, among them distributive normal forms, model sets, possible-worlds semantics, epistemic logic, doxastic logic, inductive logic, semantic information, game-theoretical semantics, interrogative approach to inquiry, and independence-friendly logic. He applied them to study problems in philosophy of language, formal epistemology, and philosophy of science. He combined systematic work with novel interpretations of important historical figures like Aristotle, Leibniz, Kant, Peirce, and Wittgenstein. Hintikka was one of the most cited analytic philosophers, and he influenced logic and philosophy also as a successful teacher and the long-time editor of the journal Synthese.