From Eugene E. Loos' Logical Relations in Discourse (amazon.com). This is from Ernst-August Gutt's essay on "Logical Relations, Relationships and Relevance":

Just dealing with these two uses, the tempting solution would be to say either that there are two homophonous suffixes -m, or that the suffix -m has two distinct senses, one marking a conjunctive relationship and the other something like an alternative relationship. However, Ivan Lowe pointed out in his introductory lectures that it is not the most helpful way to begin one's analysis: by assuming a complex solution from the start one may miss a possible simpler solution. (Loos 11).

Gutt is specifically referring to a connective in Silt'i, an Ethio-Semitic language spoken in Ethiopia. But the general principle is a good one for both lexical analysis and specifically the analysis of connectives ... like αλλα.

Don't worry, I'm not getting all gushy about relevance theory on y'all. But the principle seems like a good thing to keep in mind.