G. H. VON WRIGHT: Six Essays in Philosophical Logic. Acta Philosophica Fennica, vol. 60, Helsinki, 1996, 91 pp., ISBN 951-9264-28-0

Reviewed by
M. J. FRÁPOLLI, Departamento de Filosofía, Facultad de Psicología, 18071 Granada, Spain, e-mail: frapolli@ugr.es

As the title shows, this is a collection of six essays on philosophical logic. Three of them are devoted to analyse the possibility of building a logic of norms and the features any such logic should posses, and the other three deal with pervasive philosophical questions as the problem of colour incompatibility raised by Wittgenstein in the Tractatus, the analysis of several kinds of conditionality and nomic connections, and the rules governing the truth operator.
The paper which opens the book is called “On Colour. A logico-philosophical Fantasy” and it has not been published before. Here von Wright goes back to the problem, raised by Wittgenstein in the Tractatus, of colour incompatibility and imagines situations, cultures and languages in which it would be possible to have a system of basic attributions of colour in which they were, at the same time, primitive and independent of other attributions, making it possible the Tractarian thesis that elementary propositions are not dependent one on the others, a basic idea of logical atomism.
Dealing with the logic of norms, or deontic logic, there are three essays in which the author discusses the very possibility of such a logic and establishes some basic distinctions on this field. The paper are: “Is there a Logic of Norms?” (the English version of a paper previously published in German in 1993 and reprinted in his book Normen, Werte und Handlungen, Suhrkamp, 1994), and “On Conditional Obligation” and “Ought to be – Ought to do”, which can be considered as developments of the previous one.
The paper entitled “Conditionality” offers an analysis of conditional sentences and their relationships to the classical material conditional. The author distinguishes here between conditionality, entailment and implication, and argues for the thesis that necessarily “pÆq” (the material conditional of classical logic) and “if p, then q” (its proposed counterpart in natural languages) have identical truth conditions. Other topics touched upon in this paper are how to interpret intensional conditionals, how to accommodate causality and other nomic connections between propositions, and how to deal with counterfactuals.
The last essay on the book is called “Truth-Logics”. In it, von Wright continues the development of questions examined by him in two earlier published papers: “Truth and Logic” (Philosophical Papers, Basil Blackwell, Oxford, 1984) and “Truth, Negation and Contradiction” (Synthese, 66, 1986). Preliminary versions of “Truth-Logics” have also been published in Hungarian and Russian. The aim of this last work is to present several systems of propositional logic enriched with a truth operator (truth-logics) and to discuss their interest concerning some well-entrenched complexities in philosophy of logic, as the acknowledgement of two kinds of negation, the question of truth-value gaps, paracompleteness, paraconsistency and others, taking profit of this operator.
The author argues that the study of logic is a descriptive task, that of systematize
the principles of correct reasoning. And, although sentences used in our everyday arguments do not necessarily begin by phrases like “it is true that”, implicitly all reasoning is concerned with truth. In fact, soundness in logic is truth-preservation. All the same, von Wright does not defend the existence of the true logic, but allows that different kind of reasoning and diverse contexts might need different laws of logic. In this sense, the behaviour of the truth operator helps to determine logical relations between propositions in a variety of situations. This explains the philosophical interest of the extension of classical logic provided by truth-logic.
Six Essays in Philosophical Logic is a useful collection for any one interested in the philosophy of logic, in deontic logic and, in general, in extensions of classical logic which allow to apply it to real philosophical debates. Given the philosophical character of the author, the book is a worthy contribution also from a historical point of view.