  We study the mechanical stability of the weakly interacting Bose gas with
attractive interactions, and construct a unified picture of the collapse valid
from the low temperature condensed regime to the high temperature classical
regime. As we show, the non-condensed particles play a crucial role in
determining the region of stability, even providing a mechanism for collapse in
the non-condensed cloud. Furthermore, we demonstrate that the mechanical
instability prevents BCS-type ``pairing'' in the attractive Bose gas. We extend
our results to describe domain formation in spinor condensates.
