The paper provides a new semantics for positive modal logic using Kripke frames having a quasi ordering $\leq$ on the set of possible worlds and an accessibility relation $R$ connected to the quasi ordering by the conditions (1) that the composition of $\leq$ with $R$ is included in the composition of $R$ with $\leq$ and (2) the analogous for the inverse of $\leq$ and $R$. This semantics has an advantage over the one used by Dunn in "Positive modal logic," Studia Logica (1995) and works fine for extensions of the minimal system of normal positive modal logic.

A theorem of Sierpinski of 1919 characterized the cardinality of the continuum by means of lines in two orthogonal directions in the plane: CH if and only if there is a subset S of the plane such that every horizontal cross-section of S is countable and every vertical cross-section of S is co-countable. A theorem of Sikorski of 1951 characterizes the cardinality of an arbitrary set by means of hyperplanes in orthogonal directions in finite powers of that set. A theorem of Davies of 1962 characterizes the cardinality of the continuum by means of lines in nonorthogonal directions in the plane, which, by another theorem of Davies of 1962, may be generalized to finite-dimensional Euclidean space. The main results of this paper unify these analogous theorems of Sikorski and Davies by characterizing the cardinality of an arbitrary set by means of hyperplanes in nonorthogonal directions in that set.

We present some algebraic tools useful to the study of the expressive power of bounded formulas in second-order arithmetic (alternatively, second-order formulas in finite models). The techniques presented here come from Boolean circuit complexity and are adapted to the context of arithmetic. The purpose of this article is to expose them to a public with interests ranging from arithmetic to finite model theory. Our exposition is self-contained.

The paper presents a numerical interpretation of the quantifiers of traditional categorical propositions and then offers a generalization to accommodate all other numerical values. Next, it considers the implications possible on the basis of both minimum and maximum existential presuppositions; and finally, it shows that every pair of categorical premises yields multiple conclusions when appropriate minimum and maximum presuppositions are made for the terms of the premises.

We present an algebraic theory of structured objects based on and generalizing Aczel's theory of form systems. Notions of identity of structured objects and of transformations of systems of such objects are discussed. A generalization of Aczel's representation theorem is proven.

We consider the theory ${\rm PA}^{＃}$ and its weak fragments in the language of arithmetic expanded with the functional symbol $＃$. We prove that ${\rm PA}^{＃}$ and its weak fragments, down to $\forall E_1^{＃}({\bf N})$ and $IE_1^{-＃}$, are subject to the Tennenbaum phenomenon with respect to $+$, $\cdot$, and $＃$. For the last two theories it is still unknown if they may have nonstandard recursive models in the usual language of arithmetic.

A countable unidimensional theory without the omitting types order property (OTOP) has prime models over pairs and is hence classifiable. We show that this is not true for uncountable unidimensional theories.

From the popular view that the property of truth adds nothing not already inherent in its bearers it has been inferred that classical theories of truth are thereby refuted. Taking as representative a version of deflationism based on a certain way of interpreting the Tarskian schema convention T–and popularly called "disquotational"–I argue that the view is beset by fatal difficulties. These include: an unavoidable awkwardness in handling indexicals; an inability to accept anything more than a too anemic notion of a truth condition, leaving it defenseless against clearly inadequate alternatives; and an incapacity to show that its characteristic biconditional can support any acceptable dependency claims (made evident by replacing the biconditional with 'because'). Finally, were there no predicate on the order of 'is true', this would not annihilate the property of being true or the current grounds for philosophical inquiries about it. This is an important clue to why deflationary approaches in general are dead ends.