Johan van Benthem Deconstructing Tarski's Semantics for Predicate Logic, or: the secret world of decidable first-order logics First-order predicate logic is the general-duty tool of modern logic. Its syntax, semantics, and metatheory are well-known, and form the backbone of standard textbooks. But a price has to be paid for this broad applicability. This basic tool of the logician is undecidable, contrary to what many founding fathers may have expected. But is the price inevitable? Could things have gone differently? Returning to an earlier lunch presentation, we'll show how to analyse 'standard Tarski semantics' into a number of independent decisions, the conjunction of which leads to undecidability. Other choices turn out to generate a landscape of decidable 'predicate logics'. This insight needs no more, essentially, than a fresh closer look at what students naturally do when they show that certain predicate-logical principles are 'valid'. We'll survey some of the current technical theory in this area. We'll also discuss briefly what this deconstruction means for the usual monolithic view of 'standard logical systems'. LITERATURE J. van Benthem, 1996, "Exploring Logical Dynamics", Chapter 9, CSLI Publications, Stanford & Cambridge University Press M. Marx & Y. Venema, 1996, "Multi-Dimensional Modal Logic", Kluwer Logic Library, Kluwer Academic Publishers, Dordrecht