Some examples are a negative connotation, Don't be so negative!, or Be positive!
Is it proper to use these words this way? The denotations of negative and positive support this use weakly. However, I frequently correct people (being a semantics freak) and tell them that a negative statement is a statement that denies, while a positive statement is one that affirms.
An Ask.com question is very ambiguous on this issue. It seems that these two words are more useful in these meanings in a very casual setting.
What are the best meanings for these words, and the best words for these meanings?
How about (un)desirable or (un)favorable or eulogic/panegyric: are these words suitable alternatives for positive/negative in formal settings?