Healthy thought

Thinking, of course, depends on language.  For human thought, to a large extent, consists of speaking to oneself.   Man is a social animal, and when others are not available (and sometimes when they are available) he creates an externalized other, to whom he speaks (or thinks). In that limited sense, thinking requires multiplicity, or the creation of one other.
But, returning to the relationship between thought and language, healthy thought, and to a large extent mental health.  As is the case with clear expository writing, healthy thinking requires a diversity of thought (the or), but a certain connectivity between thoughts (the and). Disjointed thinking can take the form of mania.  However, a lack of sufficient diversity of thought, or thinking one thing over and over again, takes the form of obsessive thinking, something I know quite well.  Thus, mania is a predominance of the "or" while obsession is the predominance of the "and".  Or at least that's a start.