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What is the correct way to pluralize a proper noun like "Raspberry Pi" (a type of small, inexpensive computer)?

Would you say:

  • This project uses two Raspberry Pis
  • This project uses two Raspberry Pi's
  • This project uses two “Raspberry Pi”s

None of the options look right to me. I think the combination of being a proper noun and an unusual second word makes this tricky.

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  • 7
    "Raspberries Pi"?
    – MT_Head
    Jan 30, 2013 at 0:34
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    Related (if not duplicate): What is the plural form of “iPad 2”?
    – Callithumpian
    Jan 30, 2013 at 0:40
  • Stickler note: single digits are written as words in prose, unless those are part of the brand name etc. (thus “two of iLunch 2”).
    – theUg
    Jan 30, 2013 at 2:32
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    @theUg - You shouldn't have to apologize for being a stickler on a website dedicated to English Language & Usage. I fixed it. :)
    – Nathan Long
    Jan 30, 2013 at 3:07
  • @Callithumpian - Interesting. Taking Apple's approach, we'd always say "two Raspberry Pi computers." It does solve the pluralization problem, but seems a bit awkward.
    – Nathan Long
    Jan 30, 2013 at 3:09

3 Answers 3

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We can approach this analytically, by authority, or by observation.

Analytically

Okay, to start with our components are at least straightforward; they're both countable nouns, and the plural of raspberry is raspberries and the plural of pi is pis. We'll be using them later.

It's formed from English nouns, so there are four possible ways to treat it.

We could just not think about it, and treat it opaquely, as if Raspberry Pi were a single word. That gives us a plural of Raspberry Pis.

We could treat it as a noun adjunct, where the first noun acts as an adjective. That gives us Raspberry Pis (c.f. coffee shops).

We could threat it as a headless noun, though that seems unlikely to be correct. Anyway, this would give us Raspberry Pis.

We could treat it like a compound starting with the head, which would give us Raspberries Pi, but we'd need some strong reason to favour the first word in this manner. We can rule this out.

Of the acceptable options, since it's a pun on "Raspberry Pie", we'd favour the noun-adjunct case, but they all have the same result.

Likewise, that gives us an etymological approach: It was named to deliberately be similar to "Raspberry Pie" so we should pluralise similarly to "Raspberry Pies". That gives us Raspberry Pis.

By Authority

It was named by, and is a trademark of, The Raspberry Pi Foundation. They use the plural Raspberry Pis.

By Observation

They've been called Raspberry Pis in a variety of places.

Hence, they're Raspberry Pis.

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    Unfortunately, that form brings Manneken Pis to mind.
    – tchrist ♦
    Jan 30, 2013 at 3:13
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    Personally I like "Raspberry Pies". Incidentally, a cluster of Raspberry Pis is known as a "Bramble"
    – mgb
    Jan 30, 2013 at 3:53
  • Well, it certainly does now @tchrist.
    – terdon
    Jan 30, 2013 at 4:26
  • +1 but by observation it's not hard to find Raspberry Pi's (more than Raspberry Pis), Raspberry Pies and Raspberries Pi.
    – Hugo
    Jan 30, 2013 at 6:31
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    +1 for the thoroughness of the answer and the clarity of the conclusion.
    – TecBrat
    Apr 19, 2013 at 12:44
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As a trademark, it should be an adjective, not a noun.

This project uses two Raspberry Pi devices.

Edit: The rule that a trademark should always be an adjective comes from the International Trademark Association:

NEVER use a trademark as a noun. Always use a trademark as an adjective modifying a noun.

EXAMPLES:

  • LEGO toy blocks
  • AMSTEL beer

In the past, I have worked for large companies for whom trademarks were important, and this is one of the rules they hammered into us.

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    Trademark or no, even the creators use it as a noun (e.g. "The Raspberry Pi...") I don't know of any reason to restrict it as an adjective.
    – Lynn
    Jan 30, 2013 at 5:38
  • As a trademark it can be any part of language at all, but is more likely to be a noun than anything else. I wouldn't even read the use above as an adjective, but as a noun adjunct. Are you saying that "a Raspberry Pi", "an iPhone", "some Jell-O", "a Big Mac", "an aspirin", "an escalator", "a zipper", "some kerosene", "an apple mac" are all wrong?
    – Jon Hanna
    Jan 30, 2013 at 9:11
  • See my edit above.
    – Aric TenEyck
    Jan 30, 2013 at 14:12
  • @AricTenEyck- Interesting. Clearly you have cited a valid source, and thus I have removed by downvote. But I would point out this post which I think outlines the instances where that advice is unduly prescriptive and in contradiction with how actual companies use their own trademarks. So take it with a grain of salt.
    – Lynn
    Feb 2, 2013 at 22:46
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English already has a way to handle compound plurals like this.

Court Martial - singular
Courts Martial - plural

Attorney General - singular
Attorneys General - plural

So I would say

Raspberry Pi - singular
Raspberries Pi - plural

Simples :-)

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    Is "Raspberry Pi" really a compound word with "Raspberry" as its head? It seems to me to be a single word that can't be split. If we did try to split it, it seems to be based on "Raspberry Pie", where the head is the second word "Pie".
    – herisson
    Dec 2, 2016 at 19:15
  • The more normal way to decide acceptability with a proper name is to follow what the relevant authority (here, the company) do. If they use the plural 'RR Pudz', that's the official way. They are not bound by normal English patterning.
    – Edwin Ashworth
    Dec 2, 2016 at 19:29

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