The approach that most semanticists endorse is a combination of (1) and (4). Using techniques similar to those used by mathematicians, you can build up a complex universe of abstract objects that can serve as meanings (or denotations) of various sorts of linguistic expressions. Since sentences can be either true or false, the meanings of sentences usually involve the two truth values true and false. You can make up artificial languages for talking about these objects; some semanticists claim that these languages can be used to capture inner cognitive representations. If so, this would also incorporate elements of (3), the psychological approach to meanings. Finally, by restricting your attention to selected parts of natural language, you can often avoid hard questions about what meanings in general are. This is why this approach to some extent dodges the general question of what meanings are. The hope would be, however, that as more linguistic constructions are covered, better and more adequate representations of meaning would emerge.