My friend Janet calls it Yanksgiving. She’s referring to today—the third Thursday after the first Monday in November, when Canada’s neighbours to the south traditionally sit down to a big feast of turkey, stuffing, mashed potatoes, green bean casserole and pie. That’s what I’ll be doing today with my family. Janet—along with the rest of Canada—did her own big Thanksgiving a few weeks ago.

But it seems clear to Janet and to me that we are both celebrating Thanksgiving.

I was thinking about this earlier when I read an article in Aeon magazine about the sorites paradox. This is a paradox that asks us to imagine a heap of sand. Take away a single grain and it’s still a heap. Take away 100 grains, one by one, and it remains a heap. At some point, though, the heap must cease to be a heap. When is that moment?

I began to wonder when a Thanksgiving—or any holiday—ceases to be a holiday. Clearly, as Canadians and Americans have agreed, one can celebrate a holiday where one gives thanks for a good harvest and a good year on different days as long as one adheres to local custom. Changing the day is not the last grain of sand in the heap.

But my friend Jason recently noted on his Facebook page that if he were having a dinner party for lots of friends on any given fall evening, he’d order a bunch of Thai food or Indian food for the group in preference to making a turkey and all the fixings. Is changing the menu the equivalent of removing the defining grain of sand?

That sounds pretty persuasive until I remember that my Canadian friends are as liable to have butter tarts for dessert as pecan pie. And tourtiere, though it sounds fantastic, has never appeared next to my mom’s wild rice and cranberry sauce. So, while I’m still a little leery of Jason’s plans to get a take-away for Thanksgiving, changing the menu doesn’t destroy Thanksgiving either.

The whole question, whether we’re thinking about Thanksgiving dinners or heaps of sand, reminds me of debates about what does and does not constitute “money.” Bitcoin, for example, has no physical presence. Is that enough to make it not money? If it is, what about the salary I get twice a month. It’s deposited directly into my bank account and never takes a physical form. The bottles of beer we traded for homework help in college weren’t backed by any official system. Were they money? We certainly knew what the exchange rate was, and how the value of our money increased when the local blue laws kicked in on Sunday morning.

I don’t have a good answer, for either the ancient sorites paradox or the question of what constitutes money. I suspect that the “holidayness” of a holiday, or the “moneyness” of a particular kind of money depends a lot on tradition and on the tacit agreement of the people who interact with each other around the table or in the market.

Thanksgiving is Thanksgiving because we say it is. Money is money because we agree to use it. But what is the final grain of sand that could be removed from those heaps that would make you say, “This is no longer the thing that it was?” I expect we all have different answers. For some of us, it’s not Thanksgiving without beets or creamed onions. For some of us, it’s not money unless we can hold it in our hands.

Either way, it’s a great thing to discuss the next time you’re gathered around a table with a group of friends and family. Whatever and whenever you might be eating.