Why don’t we capitalize taxonomic names used as adjectives?

Sometimes important matters keep me up at night: how we’ll end the pandemic, how I can best contribute to the fight against climate change, what I should cook for dinner tomorrow. Other times, it’s the little mysteries.

The beautiful dragonfly above, the lined hooktail, is a member of the dragonfly family Gomphidae.  Or, if I were to phrase that differently, the lined hooktail is a beautiful gomphid dragonfly.  Did you notice the peculiarity there?  “Gomphidae” (noun), but “gomphid” (adjective). Why?

Spoiler alert: I have no idea. What’s interesting is that until very recently, I didn’t realize it was even a question. For years I’ve been correcting students (and collaborators), explaining that we capitalize dragonflies in the Gomphidae but not gomphid dragonflies (or even gomphids, with the adjective back-formed into a noun again). It was just one of those things about writing I knew so well I didn’t have to think about it. But now that I have thought about it: it doesn’t seem to make any sense. “Gomphidae” is capitalized because it’s a proper noun. Does English have proper adjectives? Of course it does*: “Indigenous”. “Canadian”. “Islamic”.

I suspect I’m not the only one who’s followed this rule without thinking about it. Consider the writing-style guide of the American Fisheries Society. In its “Capitalization” section, rule 2.15 is the familiar one: “Capitalize the names of families, orders, classes, phyla, and kingdoms and the first component of species names [that is, genus names]: Salmonidae (but salmonids)”. Right, “salmonid fishes”, and “salmonids”, lower case. But not wasting any time at all, rule 2.16 promptly contradicts rule 2.15: “Capitalize adjectives derived from proper nouns: North American”.  Look, it’s not that English orthography can’t be complex**; but by not even acknowledging the contradiction, whoever wrote the style guide is making it fairly clear they don’t understand this any more than I do. (And I’m not picking on the fish people: my efforts to find anyone explaining the issue failed.)

This is the part of the blog post where, having raising an interesting*** question, I’m supposed to answer it – ideally, with a clever connection, a fascinating historical anecdote, or the revelation of an unsuspected general rule lurking underneath. Well, with all due apologies to Winnie the Pooh, this is not That Sort Of Post. Instead, it’s the kind where I confess my utter befuddlement, and ask if anyone out there can explain to me what’s going on.  Is there a rationale for this? Am I missing something embarrassingly simple?  Over to you.

UPDATE: a couple of folks on Twitter have independently suggested that it’s because we capitalize family names not because they’re proper nouns, but because they’re “Latin” (they aren’t, actually, but they’re Latinized, so close enough).  And so when we anglicize the Latin to make the adjective form, it no longer needs capitalization.  (Here’s Larousse, explaining it this way for French; see section 3.) At first I thought this solved the problem, but of course it only moves it one step over – because we don’t, as a rule, capitalize Latin words (versus, et al., supra…).  So why would we capitalize family names (or genera, for that matter), if we didn’t consider them to be proper nouns?  (I’m trying to think of any reason we capitalize any word in English other than it being a proper noun, and I can’t.)  So I think it must remain true that we’re treating family names as proper nouns, and that means that the mystery remains.

© Stephen Heard  October 13, 2020

Image: Lined hooktail (Paragomphus lineatus) © 2010 Jee & Rani Nature Photography via Wikipedia.org CC BY-SA 4.0


*^I don’t think linguists use the term, but it’s pretty clear what it means.

**^After all, you wouldn’t capitalize “gargantuan” or “titanic”, even thought both are derived from proper nouns. Unless you made one of them back into a noun to christen an unsinkable ship, of course.

***^You’re still reading, aren’t you? Nerd.

6 thoughts on “Why don’t we capitalize taxonomic names used as adjectives?

  1. Pavel Dodonov

    Interestingly, it’s the same in Portuguese, so it’s not just something related to the English language: We say Melastomataceae but melastomatáceas. Perhaps it’s because Melastomataceae and Salmonidae are official, latin names, whereas melastomatáceas (port) or salmonids (eng) are just words imported into a language, and not official designations?

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    1. Martin

      Hi Pavel, there is a difference though: in Latin languages we do not capitilise proper adjectives: português not Português; brasileiro not Brasileiro. So it is an inherently English-lamguage problem

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  2. Manu Saunders

    oh, great question, I had not really thought of this until I read your post. Proper adjectives that can take a on an independent meaning from the source noun are often not capitalised (this post explains this nicely: https://www.glossophilia.org/2016/09/proper-adjectives-to-capitalize-or-not-to-capitalize/), but this still doesn’t work here….scientists bucking the grammar rules again! It would be interesting to see if scientists used to capitalise these in old literature and the trend has changed over time, or maybe it’s more common in some taxonomic groups. Now that I think about it, I see eucalypt and Eucalypt both used, and pretty sure I have used both myself without thinking..

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  3. Donald ZEPP

    My being always happy to speculate from a position of complete ignorance, I herewith share my notion that the singular forms of family names are best not being forced into use as substantives, retaining instead their adjectival purpose (and thereby remaining consistent with their lower case).

    Admittedly, zoölogical family names are completely adjectival in form, the plural suffix “-idae” referring to a likeness or similarity. This plural use refers to animals all of which in some way resemble the type genus, and resultant families are therefore exclusive–if malleable–groups. Such defined group names are reasonably used as substantive, collective proper nouns.

    Conversely, the singular of the same suffix, “-id,” is not at all collective, referring instead to some aspect(s) of a single, sub-family taxon. Nonetheless, through linguistic convention, we often take a shortcut and say “That’s a culicid,” rather than the more accurate “That’s a culicid species”

    So, in brief (or is it too late?), I’m guessing that retention of the lower case could simply be a holdover of the singular adjectives’ trying desperately to retain their decidedly descriptive usage and–despite English’s penchant for capitalized demonyms–showing their disdain for being used as substantives in the singular.

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