---------------------------------------- S12c. What is the role of quantum logic? ---------------------------------------- Quantum logic is a variant of logic often thought to be appropriate for the foundations of quantum mechanics. A good exposition is given in K. Svozil, Quantum Logic, Springer, Singapore 1998. The book is nice and useful for its material on hidden-variable related arguments. However, all that is commonly argued in textbooks about QM is argued in terms of classical logic. An even cursory look at the large quantum mechanical literature reveals that quantum logic only has a marginal spectator role in QM, while all proofs of all properties of quantum systems have always been discussed using the familiar classical logic. Even in Svozil's book, one can see that quantum logic is argued in terms of classical logic, and that it has essentially no role in the analysis of actual physical situations (apart from those used for testing the foundations). Beyond a certain point, quantum logic is sterile, which is the reason it never figures in textbooks (except perhaps in passing). All one ever needs to know about quantum logic (unless one wants to specialize in it) is summarized in Sections 6 and 7 of my paper Int. J. Mod. Phys. B 17 (2003), 2937-2980 = quant-ph/0303047.