This paper is a study of Brentano’s ontology, and more specifically of his theory of substance and accident as put forward toward the end of his life in the materials collected together as the Kategorienlehre or Theory of Categories. Here Brentano presents an auditious (re-)interpretation of Aristotle’s theory of substance and accidence. We show that on the Brentano initially defends, it is space which serves as the single substance upon which all other entities depend as accidents of space. In an (...) appendix, however, Brentano puts forward an even more radical suggestion, inspired by the physics of Kelvin. According to this final view, space itself is an accident of a deeper substance: the present time. (shrink)

In this presentation, I first outline three different notions of concepts: one derives from Leibniz, while the other two derive from Frege. The Leibnizian notion is the subject of his “calculus of concepts” (which is really an algebra). One notion of concept from Frege is what we would call a “property”, so that when Frege says “x falls under the concept F”, we would say “x instantiates F” or “x exemplifies F”. The other notion of concept from Frege is that (...) of the notion of sense, which played various roles within Frege's theory. This notion of concept can be generalized and, as such, accounts for our intuitive talk of “x's concept of …”, where the ellipsis can be filled in with a name for individual, a property, or a relation, etc. After outlining these three notions, I then discuss how (axiomatic) object theory offers a distinct, precise regimentation of each of the three notions. (shrink)

Is there an explanation of why the state of x's bearing the non-symmetric binary relation R to y is different from its differential opposite, the state of y's bearing R to x? One traditional view has it that the explanation is that non-symmetric relations hold of objects in an essentially directional way, ordering the relevant relata. We call this view ‘directionalism’. Kit Fine has suggested that this approach is subject to significant metaphysical difficulties, sufficient to motivate seeking an alternative analysis. (...) He considers two such alternative explanations, which he labels ‘positionalism’ and ‘anti-positionalism’. Of these he endorses the latter. We argue that anti-positionalism fails to provide a coherent explanation of the distinction between differential opposites, and that one should simply hold the minimalist position that there is no explanation for this metaphysical difference. (shrink)

In common treatments of deontic logic, the obligatory is what is true in all deontically ideal possible worlds. In this article, I offer a new semantics for Standard Deontic Logic with Leibnizian intensions rather than possible worlds. Even though the new semantics furnishes models that resemble Venn diagrams, the semantics captures the strong soundness and completeness of Standard Deontic Logic. Since, unlike possible worlds, many Leibnizian intensions are not maximally consistent entities, we can amend the semantics to invalidate the inference (...) rule which ensures that all tautologies are obligatory. I sketch this amended semantics to show how it invalidates the rule in a new way. (shrink)

Quine’s most important charge against second-, and more generally, higher-order logic is that it carries massive existential commitments. The force of this charge does not depend upon Quine’s questionable assimilation of second-order logic to set theory. Even if we take second-order variables to range over properties, rather than sets, the charge remains in force, as long as properties are individuated purely extensionally. I argue that if we interpret them as ranging over properties more reasonably construed, in accordance with an abundant (...) or deflationary conception, Quine’s charge can be resisted. This interpretation need not be seen as precluding the use of model-theoretic semantics for second-order languages; but it will preclude the use of the standard semantics, along with the more general Henkin semantics, of which it is a special case. To that extent, the approach I recommend has revisionary implications which some may find unpalatable; it is, however, compatible with the quite different special case in which the second-order variables are taken to range over definable subsets of the first-order domain, and with respect to such a semantics, some important metalogical results obtainable under the standard semantics may still be obtained. In my final section, I discuss the relations between second-order logic, interpreted as I recommend, and a strong version of schematic ancestral logic promoted in recent work by Richard Heck. I argue that while there is an interpretation on which Heck’s logic can be contrasted with second-order logic as standardly interpreted, when it is so interpreted, its differences from the more modest form of second-order logic I advocate are much less substantial, and may be largely presentational. (shrink)

Leibniz’ principal doctrine of truth is an attempt to set out the truth-conditions for a certain syntactically-defined class of propositions. As such, it constitutes an attempt to provide at least one portion of a semantical theory. The doctrine itself is found for example in Elementa Calculi:Every true categorical proposition, affirmative and universal, signifies nothing but a certain connection between the predicate and the subject… This connection is such that the predicate is said to be in the subject, or to be (...) contained in it, and this either absolutely and viewed in itself, or in some particular case. Or in the same way, the subject is said to contain the predicate; that is, the notion of the subject, either in itself or with some addition, involves the notion of the predicate.It is clear, from this work as well as from “First Truths” and “On Freedom”, that the doctrine is not restricted to universal affirmatives, but applies as well to particular affirmatives. (shrink)

This essay critically examines a widely held assumption in interpreting Leibniz's modal metaphysics: that whatever is necessarily actual is necessary. I argue that Leibniz rejected this axiom for principled reasons having to do with his views on the grounding of metaphysical modalities in divine power and intellect (but not divine will). I also argue that if we read him in light of this rejection, his per se possibility theory becomes (contrary to its reception in the literature) quite successful in addressing (...) the problem of necessitarianism. (shrink)

Greek antiquity saw the development of two distinct systems of logic: Aristotle’s theory of the categorical syllogism and the Stoic theory of the hypothetical syllogism. Some ancient logicians argued that hypothetical syllogistic is more fundamental than categorical syllogistic on the grounds that the latter relies on modes of propositional reasoning such asreductio ad absurdum. Peripatetic logicians, by contrast, sought to establish the priority of categorical over hypothetical syllogistic by reducing various modes of propositional reasoning to categorical form. In the 17th (...) century, this Peripatetic program of reducing hypothetical to categorical logic was championed by Gottfried Wilhelm Leibniz. In an essay titledSpecimina calculi rationalis, Leibniz develops a theory of propositional terms that allows him to derive the rule ofreductio ad absurdumin a purely categorical calculus in which every proposition is of the formA is B. We reconstruct Leibniz’s categorical calculus and show that it is strong enough to establish not only the rule ofreductio ad absurdum, but all the laws of classical propositional logic. Moreover, we show that the propositional logic generated by the nonmonotonic variant of Leibniz’s categorical calculus is a natural system of relevance logic known as RMI$_{{}_ \to ^\neg }$. (shrink)

The “official” history of connexive logic was written in 2012 by Storrs McCall who argued that connexive logic was founded by ancient logicians like Aristotle, Chrysippus, and Boethius; that it was further developed by medieval logicians like Abelard, Kilwardby, and Paul of Venice; and that it was rediscovered in the 19th and twentieth century by Lewis Carroll, Hugh MacColl, Frank P. Ramsey, and Everett J. Nelson. From 1960 onwards, connexive logic was finally transformed into non-classical calculi which partly concur with (...) systems of relevance logic and paraconsistent logic. In this paper it will be argued that McCall’s historical analysis is fundamentally mistaken since it doesn’t take into account two versions of connexivism. While “humble” connexivism maintains that connexive properties only apply to “normal” antecedents, “hardcore” connexivism insists that they also hold for “abnormal” propositions. It is shown that the overwhelming majority of the forerunners of connexive logic were only “humble” connexivists. Their ideas concerning connexive implication don’t give rise, however, to anything like a non-classical logic. (shrink)

R. C. Sleigh's Leibniz and Arnauld: A Commentary on Their Correspondence is a very good book: it is detailed, clearly written, well argued and attentive to the historical background. The more I read it, the more I enjoyed it and the more I learned. Not only does it offer a wide variety of interesting points for the reader to agree and disagree with, it has, also, the virtue of pretty well forcing the reader to think about the issues involved and (...) their connection with a variety of other philosophical problems. It breaks a good deal of new ground and, as is the way with new ground-breaking, it sometimes only scratches the surface: it points out both the need for further, more detailed investigations and the way in which such investigations might fruitfully proceed. By and large, however, it does a great deal more than scratch the surface: its depth of discussion is such that only a comparably sized book could hope to discuss in all their ramifications the problems raised by Sleigh. (shrink)

“Logic” entails both a toolkit for dealing with situations requiring precision, and a prescription for a type of public reasoning. A sufficiently extended society facing a stream of genuinely novel opportunities and challenges will benefit from an ability to generate and encourage the use of such reasoning systems to deal with these opportunities and challenges. The study of “logic” is the result of using the toolkit on itself, which would appear to be a necessary and not unnatural step for a (...) society developing sufficient familiarity with the toolkit. Many societies have developed something like logic, and past and present use of logic-like toolkits in learning situations and transmission of skills suggests that many societies will develop something like logic. (shrink)