I understand that the phrase "positive statement" means, when opposed to normative statement (like in economics), statements that describe facts without indicating (dis)approval, thus that are objective. For example This chair is blue is positive, while It'd be better if this chair were blue is normative. (Edit: please note that this has nothing to do with its being true or not. In this context, "This chair is blue" is treated as a positive statement regardless of the colour of the chair.)
I don't quite understand why the word "positive" is chosen in this phrase. When I refer to an English thesaurus, I get affirmative, favourable, constructive, optimistic, certain, sure, etc. as synonyms, but none of them seem to fit in this context.
Which meaning of positive makes this word suitable to be used in contrast to normative statement?
Edit: as @Mitch pointed out, these seem to be technical meanings. Let me provide more context below.
I (non-native speaker) encountered the usages of "positive statement: in my introductory economics class, and according to the professor, they are terms mostly used in the context of philosophy of science and in economics. page titled "Introduction to Environmental Economics and Policy" in soas.ac.uk provides similar usage. Quating:
Normative statements derive from an opinion or a point of view. Thus the words 'should', 'ought to' or 'it is better to' frequently occur. The validity of normative statements can never be tested. Positive statements, on the other hand, can be tested, at least in theory, if not always in practice.
In the lecture I'm receiving, other usages of this "positive" includes positive exclusion of markets vs normative exclusion of markets, where the former means "markets are not capable of this" and the latter means "We don't want markets to do this".