Language is used to express thought, but sometimes the terms we use get in the way of proper analysis of the situation. One situation so impaired is discussion of "the homeless." Use of a single term for everyone without a permanent residence tends to obscure the fact that different people are in that situation for very different reasons, and different causes call for different solutions.  There are at least three subgroups, sometimes called the "have nots," the "cannots," and the "will nots."

C.W. Nevius has this sad story in the SF Chron on one of the "cannots." For this subgroup, homelessness is just one facet of what is fundamentally a mental health issue.