Reading grammars for more information on αλλα, I came across this paragraph from Funk's Hellenistic Grammar, §611 (Chapter 41, "Function Words/Negatives":

Negatives, conjunctions, sentence connectors, and subordinators may be termed function words (Fries: 87-109) or structure signaling words (Roberts, 1958: 151f., 224ff.). The point of these labels is that such words are nearly lexically empty, i.e. they have little or no dictionary meaning of their own. However, they are grammatically significant in indicating the structure of sentences and parts of sentences (cf. §§001ff.). Some of them are so common as to require acquaintance at the grossest level of the language. This simply means that one must learn how they function early in the process. One may guess at the meaning of lexically full words, or leave them blank when reading (cf. §003), but one must know the grammatical "meaning" of function words to be able to proceed at all. It is the case, of course, that some function words are  more pervasive and significant than others. (Funk 475, bold added)

I think this statement from Funk gets at the problem that most people have when approaching conjunctions. They approach them as "lexically full" words. Words that have a reliable and relatively consistent translation.

But they don't. As Funk writes, they're "lexically empty". They have oodles of grammatical meaning and tons of information to shed on how the text is read, but they have no reliable functional equivalent. If our approach to conjunctions is like:

• δε means "but"
• και means "and" (except for when it means "also")
• ουν means "therefore"
• γαρ means "for"
• αλλα means "but" (but it's a stronger 'but' than δε, of course)
• etc., etc.

Then it's no big surprise that we miss so much when we attempt to stitch our glossed-up English word-swapping into something coherent that truly represents the Greek we're supposedly translating (but more realistically, we're decoding). I say this knowing I'm as guilty (or more guilty) of it as the next person; I'm not innocent here.

What's the way out of the slough of despond? Buck up, Pilgrim, because Funk hints at it in this very paragraph: "This simply means that one must learn how [function words] function early in the process."

So the answer is, "early in the process", to pay attention to how these words work; not so that you know what to put in the blank on next week's vocab/translation test, or so you know what to slide in when you do on-the-fly translation in your next reading class, or so that you know which words to ignore when you're choosing the 'important' words from next week's sermon text, but so that you can understand what the author/writer is communicating. Because that is the goal. Right?

(side note: That last "but" ... it would be an αλλα if that was Greek, not a δε.)