This half-pound bag of Blue Bottle Coffee is a begat.

According to my father-in-law Ed, who knows a bit of Yiddish, many things that are bought may fit into the category he calls “begat.” And even though “begat” begins its life as a verb — beget, which means to sire or cause to exist — here it’s used, in its past tense, as a noun. Most simply put, a begat is a purchase that begets another purchase. Like, the new couch that begets the purchase of a new area rug. (Indeed, according to Ed, a new couch is the classic begat.)

Sometimes, we make purchases so innocently: “Oh, all I need is a chair for this corner, and then the room will be complete.” A day after the chair arrives, we find ourselves pacing the aisles of Home Goods, looking for a few pillows that will “tie in” the new chair to the old furniture. The new pillows, in turn, may function as a begat and lead to a new lump of pottery on the table. Which could make us rethink the floor lamp in the corner. The new lamp is an opportunity to try the innovative, energy-saving compact fluorescent light bulbs. Why not buy a dozen? And so on and on and on.

Back to the meager bag of coffee. I bought it in San Francisco, as I stood in line with Steve at one of Blue Bottle’s stands. He and Marcia had been telling me for days: This is the thing, if you like coffee. So, finally, on the last day of my visit, we went. Steve had already told me that Blue Bottle was not just a coffee; it was a method. Nay, it was a way. I was fully prepared, and eager.

We ordered. I stood near the register and waited to pay. I looked at the display of brown bags plump with beans. As I held out my cash, I said to the guy, “If I buy some of these beans, can you grind them for me?”

He held out his hand, took the twenty, and coolly returned my gaze. In so many words, he explained that they didn’t grind for customers: “You really have to grind this at home, if you want the full freshness.”

Hmm. I only hesitated a moment. “Well, I don’t have a grinder — I brought it to work years ago and it disappeared — but I’ll buy one.” Really, on the spot I decided to buy a grinder when I got home.

The 8 ounces of Blue Bottle’s Bella Donovan was about $8 in San Francisco. Three days ago, back in Boston, I did buy a new coffee grinder; it was $30 on sale. And while I was in the small appliances section, I looked at coffee makers, too. After all, mine is old, on its seventh life, and almost uncleanable. Yes, I did. New coffee maker: $80 on sale. Next? Cups.

That is the story of a begat.