  Collapse theories are versions of quantum mechanics according to which the
collapse of the wave function is a real physical process. They propose precise
mathematical laws to govern this process and to replace the vague conventional
prescription that a collapse occurs whenever an "observer" makes a
"measurement." The "primitive ontology" of a theory (more or less what Bell
called the "local beables") are the variables in the theory that represent
matter in space-time. There is no consensus about whether collapse theories
need to introduce a primitive ontology as part of their definition. I make some
remarks on this question and point out that certain paradoxes about collapse
theories are absent if a primitive ontology is introduced.
