The idea of a marriage engagement is kind of weird. On its face, it seems to be a promise to make a promise: the two people promise each other to exchange marriage vows. But if you’re promising to promise X, why don’t you just promise X right away?
I think there are two ways to save the idea of engagement given the above. One can raise the level of the marriage commitment or one can lower the level of engagement commitment.
The first approach would be to say that the marriage vows aren’t mere promises: they are vows, a covenant. A vow has a different, qualitatively higher--even sacred--binding force than a mere promise. If this is right, then we can learn something from the cultural practice of engagement, something about the higher level of normative commitment in marriage.
The second approach would be to demote engagement. Perhaps we can look at an engagement as akin to what the business world calls a “non-binding agreement in principle”.
