Exogenous depression, on the other hand, can be treated with talk therapy because the root is in some sort of pathological thinking.
A bit off-topic here, but I just want to briefly say something about what SOC said here, because it's a subject that I really care about... Personally, I don't think it's helpful to think of reactive depression as being caused by 'pathological thinking', but I think it's better to think of it as a neurochemical, or psychological, reaction to external stimuli or stress. The mental processes that lead to depression can be at a subconscious or emotional level, and don't necessarily involve conscious thoughts. I know what SOC was getting at though, as talking therapies can help ease reactive depression, and some talking therapies address habitual 'thinking' processes, which can in turn change our attitudes and coping mechanisms that can lead to depression.