Can OUGHT be derived from IS? This book presents an investigation of this time-honored problem by means of alethic-deontic predicate logic. New in this study is the leitmotif of relevance: is-ought inferences indeed exist, but they are all irrelevant in a precise logical sense. New proof techniques establish this result for very broad classes of logics. A profound philosophical analysis of is-ought bridge principles supplements the logical study. The final results imply incisive limitations for the justifiability of ethics as opposed to empirical science.

1. Philosophical Background and Program of the Study.- 2. The Logical Background: A.D.1-Logics.- 3. The Logical Explication of Hume's Thesis.- 4. The General Hume Thesis GH.- 5. The Special Hume Thesis SH.- 6. Weakened Versions of Hume's Thesis in A.D.I-Logics with Bridge Principles.- 7. A.D.1-Logics with Weak Alethic Fragments: ? as a Subjective Propositional Attitude.- 8. Generalizations.- 9. Some Applications to Ethical Arguments.- 10. The Problems of Identity and Existence.- 11. Are There Analytic Bridge Principles? A Philosophical Investigation.- 12. Are Synthetic Bridge Principles Scientifically Justifiable?.- A.1 Interchange of substitution for predicates and for individual variables.- A.2 Transitivity of predicate substitutions.- A.5 Preservation of frame-validity under ?-substitution.- A.6 Advancing ?-, a- and d-rule.- A.7 Model-completeness for a.d.l-logics.- A.8 Singleton frames for a.d.1-logics which are not propositionally representable.- A.9 Canonical a.0-logics with incomplete 1-counterparts.- A.10 Canonicity transfer from a.0- to a.1-logics.- A.11 Canonicity transfer from monomodal to combined bimodal 1-logics.- A.12 Halldéncompleteness and the Bolzano-criterion.- A.13 Correspondence and canonicity for (N1-5).- A.14 Domains of j.1.-models.- A.16 Characterization of a.d.(G)2-logics.- A.17 Admissibility of (?GR).- Table of Definitions, Lemmata, Propositions, Theorems, Corollaries, Facts, Figures and Problems.- Notes.