  Modal interpretations of quantum mechanics were designed to solve the measurement problem and to reconcile quantum mechanics with relativity. They are no-collapse, (typically) indeterministic hidden-variables theories.  Quantum-mechanical states of systems (which may be construed as denoting their states or information about these states) always evolve according to unitary and linear dynamical equations (the Schrödinger equation in the non-relativistic case). And the orthodox quantum-mechanical state description of systems is supplemented by a set of properties, which depends on the quantum-mechanical state and which is supposed to be rich enough to account for the occurrence of definite macroscopic events and their classical-like behavior, but sufficiently restricted to escape all the known no-hidden-variables theorems. (For modal interpretations, see van Fraassen 1973, 1981, 1991, chapter 9, Kochen 1985, Krips 1987, Dieks 1988, 1989, Healey 1989, Bub 1992, 1994, 1997, Vermaas and Dieks 1995, Clifton 1995, Bacciagaluppi 1996, Bacciagaluppi and Hemmo 1996, Bub and Clifton 1996, Hemmo 1996b, Bacciagaluppi and Dickson 1999, Clifton 2000, Spekkens and Sipe 2001a,b, Bene and Dieks 2002, and Berkovitz and Hemmo 2006a,b. For an entry-level review, see the entry on modal interpretations of quantum theory. For comprehensive reviews and analyses of modal interpretations, see Bacciagaluppi 1996, Hemmo 1996a, chapters 1-3, Dieks and Vermaas 1998, Vermaas 1999, and the entry on modal interpretations of quantum theory. For the no-hidden-variables theorems, see Kochen and Specker 1967, Greenberger, Horne and Zeilinger 1989, Mermin 1990 and the entry on the Kochen-Specker   theorem.)[21]