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.

Preface. 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 Human Thesis SH. 6. Weakened Vesions of Hume's Thesis in A.D. 1- 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? Appendix. Notes. Bibliography.