This sign is behind glass, so I’ll clarify what it says: “LET US SHIP YOUR LUGGAGE.”

Let us ship your luggage.

When I saw this sign, my first thought was  “great idea, but I’ll probably have to mortgage the co-op to take advantage of this service.” My second thought was “why is let us different from let’s?” A sign reading “Let’s ship your luggage” is an invitation to a playdate. We’ll get together, have some wine, and then take turns sticking labels on suitcases. Yet contractions – shortened versions of words or phrases in which an apostrophe takes the place of missing letters – are supposed to mean the same as the full-length expressions they replace. So why is it that when people say, “Let’s do the wash,” they aren’t offering to take a chore off my hands, but a sign saying, “Let us do the wash” excludes me from responsibility? Perhaps the contraction includes the speaker and the person/people addressed, and the full-length version doesn’t.

This was my favorite theory on the difference between “let’s” and “let us,” until I thought of church. When a preacher says, “Let us pray,” everyone is supposed to participate – both preacher and congregation. (I can’t picture a member of the clergy saying, “Let’s pray,” now that the Sixties are over and guitars and interpretive dances have fallen out of favor in religious rites.)

My third thought, in case you’re counting, is that the contraction creates an air of friendship and the unshortened expression adds a sense of formality. The shopkeeper offering to ship luggage or do the laundry is engaged in a commercial transaction. The preacher is acting in an official capacity, calling the congregation to prayer.

Is this the final word on “let’s” and “let us”? Let’s wait and see.