# 3 is to "Trilogy" as 2 is to ... um ... **URL:** \ **Category:** Factual Questions\ **Created:** [April 5, 2004, 8:00am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323 "2004-04-05T08:00:14Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![choie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/choie/32/7829_2.png) [@choie](https://boards.straightdope.com/u/choie)\ **Post date:** [April 5, 2004, 8:00am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/1 "2004-04-05T08:00:14Z")
_Disclaimer: I’m fully aware that this is a really lame question. I can’t tell if the reason I’m unable to figure it out for myself is premature senility, selective amnesia or an embarrassing display of ignorance. But whatever the cause of this mental lapse, I do need to know the answer … so here goes nuthin’._ In describing a series of three related books, films, recordings, etc., we use the term “trilogy,” right? Well, what the heck is the equivalent term for a set of two books/films/whatever? “Duology” would be the logical choice – if it were really a word! But a quick search turned up no mainstream groundswell of support for the term … apart from some Star Wars and other Sci-Fi or Fantasy book series publishers. Okay, what’s left? Duo? Too unpretentious, and like “Duet” sorta implies two things that occur simultaneously. Pairing? Couple? Twosome? Meh. Couplet? Ick. Sigh. Believe it or not I’m normally considered quite word-savvy. And yet I’m coming up woefully blank on this. I feel as if I’m missing the obvious, that the answer’s as plain as the nose on my face … ARRGH! Logophiles, help me! ---
**Author:** ![netscape\_6](https://avatars.discourse-cdn.com/v4/letter/n/8c91f0/32.png) [@netscape\_6](https://boards.straightdope.com/u/netscape_6)\ **Post date:** [April 5, 2004, 8:02am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/2 "2004-04-05T08:02:47Z")
Duo comes to mind. Remember the greatest duo’s always come in pairs. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 5, 2004, 8:22am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/3 "2004-04-05T08:22:45Z")
[Thesaurus.com](http://Thesaurus.com) doesn’t offer much help either; could it be that the rarity or absence of a specific term reflects the rarity of stories/books/films that are _concieved_ as two-part entities (by which I specifically mean to exclude those that have a sequel tacked on as an afterthought)? There’s something psychologically necessary, I think, about a trilogy. So duology may actually be the best you’ll get (or invent). ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [April 5, 2004, 8:28am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/4 "2004-04-05T08:28:57Z")
I’ve actually heard duology used in this sense. My attempt to subvert the meaning of “biology” has, so far, met with failure. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 5, 2004, 9:36am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/5 "2004-04-05T09:36:29Z")
> [@choie](#): > > In describing a series of three related books, films, recordings, etc., we use the term “trilogy,” right? Well, what the heck is the equivalent term for a set of two books/films/whatever? > > “Duology” would be the logical choice – if it were really a word! But a quick search turned up no mainstream groundswell of support for the term … apart from some Star Wars and other Sci-Fi or Fantasy book series publishers. Actually, I’d be extremely loath to say “duology”. In general, I work from the premise that similar kinds of prefices should be used. Where else does tri- show up? Well, the first easy answer is “triangle”, but that’s not much help because there really aren’t any two-sided polygons (those of you who know what people say nowadays, hush up. I’m getting to that). What else? “Tricycle” is a nice one that comes to mind. A tricycle has three wheels. What has two? A bicycle! Thus, whenever I want to move from a word using tri- to express “threeness” to a similar word expressing “twoness”, I’ll go for bi-. Thus: bilogy. ---
**Author:** ![alterego](https://avatars.discourse-cdn.com/v4/letter/a/6bbea6/32.png) [@alterego](https://boards.straightdope.com/u/alterego)\ **Post date:** [April 5, 2004, 10:19am UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/6 "2004-04-05T10:19:37Z")
bilogy? I belive you would call it a two-part series. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [April 5, 2004, 1:46pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/7 "2004-04-05T13:46:47Z")
A stretch, but you could call it a “diptych.” (Though it really refers to pictures.) > **[Definition of DIPTYCH](https://www.merriam-webster.com/dictionary/diptych)** > > a 2-leaved hinged tablet folding together to protect writing on its waxed surfaces; a picture or series of pictures (such as an altarpiece) painted or carved on two hinged tablets; a work made up of two matching parts… See the full definition Main Entry: dip·tych Pronunciation: 'dip-(")tik Function: noun Etymology: Late Latin diptycha, plural, from Greek, from neuter plural of diptychos folded in two, from di- + ptychE fold 1 : a 2-leaved hinged tablet folding together to protect writing on its waxed surfaces 2 : a picture or series of pictures (as an altarpiece) painted or carved on two hinged tablets 3 : a work made up of two matching parts ---
**Author:** ![leenmi](https://avatars.discourse-cdn.com/v4/letter/l/f1d935/32.png) [@leenmi](https://boards.straightdope.com/u/leenmi)\ **Post date:** [April 5, 2004, 2:13pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/8 "2004-04-05T14:13:26Z")
a book and its sequel. Or prequel, depending. If they are big enough books, you might call them a saga. If they are grand enough, it might be an epic saga. ---
**Author:** ![Ross](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@Ross](https://boards.straightdope.com/u/Ross)\ **Post date:** [April 5, 2004, 3:00pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/9 "2004-04-05T15:00:30Z")
“Brace”? Another one for the “no” pile I suppose. ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 5, 2004, 3:03pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/10 "2004-04-05T15:03:20Z")
> [@alterego](#): > > bilogy? > > I belive you would call it a two-part series. Well yes, but that’s hardly a parallel term. I’m sure the OP could figure that much out. ---
**Author:** ![Orbifold](https://avatars.discourse-cdn.com/v4/letter/o/779978/32.png) [@Orbifold](https://boards.straightdope.com/u/Orbifold)\ **Post date:** [April 5, 2004, 4:05pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/11 "2004-04-05T16:05:36Z")
> [@Mathochist](#): > > Where else does tri- show up? > > Well, the first easy answer is “triangle”, but that’s not much help because there really aren’t any two-sided polygons (those of you who know what people say nowadays, hush up. I’m getting to that). [hijack] Actually, what mathematicians commonly call a two-sided polygon is actually grammatically…well, maybe not wrong, but certainly odd. The commonly used mathematical term is in fact “bigon”. Which is a shame because “bi-” is a Latin prefix, while “-gon” is a Greek suffix. The correct term for a two-sided polygon should be either “digon” (all Greek" or “bilateral” (all Latin). [/hijack] This raises the question regarding the OP: is “-logy” a suffix with Latin origins or Greek origins? I’m guessing Greek, given the similarity with “logos”, but that’s just a guess. If it is Greek, then I would argue for the word “dilogy”. ---
**Author:** ![Shrinking\_Violet](https://avatars.discourse-cdn.com/v4/letter/s/df705f/32.png) [@Shrinking\_Violet](https://boards.straightdope.com/u/Shrinking_Violet)\ **Post date:** [April 5, 2004, 4:12pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/12 "2004-04-05T16:12:25Z")
Referring to hard-copy Roget’s Thesaurus and Chambers Dictionary … “dyad”? _“A pair of units treated as one”_ ---
**Author:** ![Meeko](https://avatars.discourse-cdn.com/v4/letter/m/e495f1/32.png) [@Meeko](https://boards.straightdope.com/u/Meeko)\ **Post date:** [April 5, 2004, 4:14pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/13 "2004-04-05T16:14:56Z")
On a related note, the ‘people’ behind the marketing of the Aliens “Quadrillogy” here in the US made up that word. I heard someone speaking to this fact, and I beleive he supplied the correct term. I do not recall what it is at this moment, but in fact there is a term… so I think that since 4 is covered, 2 would most definately be covered. The name for 2 in a group when compared to a Trilogy was not discussed. Also, There are a LOT of Trilogies out there, Matrix, Star Wars, LOTR, Terminator to name a few. I suspect the term is out there for the 2 grouping… but its crowded out by the sheer volume of the trilogy usage. ---
**Author:** ![Orbifold](https://avatars.discourse-cdn.com/v4/letter/o/779978/32.png) [@Orbifold](https://boards.straightdope.com/u/Orbifold)\ **Post date:** [April 5, 2004, 4:43pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/14 "2004-04-05T16:43:19Z")
> [@Meeko](#): > > On a related note, the ‘people’ behind the marketing of the Aliens “Quadrillogy” here in the US made up that word. I heard someone speaking to this fact, and I beleive he supplied the correct term. I do not recall what it is at this moment, but in fact there is a term… Tetralogy? “Tetra-” being the Greek prefix for four, as in “tetrahedron”. ---
**Author:** ![Steve\_Wright](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@Steve\_Wright](https://boards.straightdope.com/u/Steve_Wright)\ **Post date:** [April 5, 2004, 5:35pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/15 "2004-04-05T17:35:01Z")
“Tetralogy” is a perfectly respectable word, and the right one for a set of four books. Or movies, I guess. Dates from the seventeenth century, according to my Oxford Dictionary of English Etymology, which of course is my constant bedside reading companion. It’s Greek in origin, of course - ultimately from _logos_, “word”, plus the appropriate number in prefix form. I don’t find either “bilogy” or “dilogy” in the ODEE, though. ---
**Author:** ![Qwisp](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qwisp/32/397_2.png) [@Qwisp](https://boards.straightdope.com/u/Qwisp)\ **Post date:** [April 5, 2004, 5:40pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/16 "2004-04-05T17:40:55Z")
> [@leenmi](#): > > a book and its sequel. Or prequel, depending. > > If they are big enough books, you might call them a saga. > > If they are grand enough, it might be an epic saga. I agree that you would use sequel, nothing else would be the correct term in the OP situation ---
**Author:** ![choie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/choie/32/7829_2.png) [@choie](https://boards.straightdope.com/u/choie)\ **Post date:** [April 5, 2004, 7:09pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/17 "2004-04-05T19:09:43Z")
Hey thanks, everyone! Now I feel a little bit better about not being able to think of this word, since apparently … there ain’t one. 🙂 Ooh, if I were writing this article on my own, I’d definitely go with “diptych.” It’s just slightly over the head of my target audience, but I like to make 'em look things up. However, since I’m just editing/rewriting, I need to keep within the original author’s casual style. (He’s already overused “two-parter,” so I’m trying to add a little variety.) I get the etymology of “bilogy,” but … it sounds like a disease that some nasty tabloid writers might have. 😉 I’ll continue to mull over your suggestions. Many thanks again to those who’ve responded so far! ---
**Author:** ![Dahnlor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dahnlor/32/533_2.png) [@Dahnlor](https://boards.straightdope.com/u/Dahnlor)\ **Post date:** [April 5, 2004, 8:00pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/18 "2004-04-05T20:00:08Z")
> [@Orbifold](#): > > [hijack] > > Actually, what mathematicians commonly call a two-sided polygon is actually grammatically…well, maybe not wrong, but certainly odd. The commonly used mathematical term is in fact “bigon”. Which is a shame because “bi-” is a Latin prefix, while “-gon” is a Greek suffix. The correct term for a two-sided polygon should be either “digon” (all Greek" or “bilateral” (all Latin). > > [/hijack] It strikes me as odd that such a word even exists, considering that there’s no such thing as a two-sided polygon (unless you consider an open angle as one). It would look like a line (or vector) which is a one-dimensional object. Then again, I guess we could just let bigons be bigons. 😃 D ---
**Author:** ![Orbifold](https://avatars.discourse-cdn.com/v4/letter/o/779978/32.png) [@Orbifold](https://boards.straightdope.com/u/Orbifold)\ **Post date:** [April 5, 2004, 8:45pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/19 "2004-04-05T20:45:09Z")
> [@Dahnlor](#): > > It strikes me as odd that such a word even exists, considering that there’s no such thing as a two-sided polygon (unless you consider an open angle as one). There’s no such thing a two-sided polygon in Euclidean geometry, but some non-Euclidean geometries do allow such a beast. Spherical geometry, for example: on the surface of the Earth any two different lines of longitude form a bigon with one vertex at each pole. > [@](#): > > Then again, I guess we could just let bigons be bigons. 😃 No comment 🙂 ---
**Author:** ![Mathochist](https://avatars.discourse-cdn.com/v4/letter/m/c89c15/32.png) [@Mathochist](https://boards.straightdope.com/u/Mathochist)\ **Post date:** [April 5, 2004, 9:07pm UTC](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323/20 "2004-04-05T21:07:54Z")
> [@Orbifold](#): > > This raises the question regarding the OP: is “-logy” a suffix with Latin origins or Greek origins? I’m guessing Greek, given the similarity with “logos”, but that’s just a guess. If it is Greek, then I would argue for the word “dilogy”. Didn’t I say hush up? Actually, this reminds me of a play I saw once (can’t remember the title) which was basically a fictionalized bio of D.H. Lawrence. He was (it’s now thought) gay before there was really any standard term for it. Near the end there’s a scene where one of his more activist friends notes “Did you hear? They’ve got a term for people like us now. ‘Homosexual’.” “Oh, that’s just _awful_.” “What? I think it’s a wonderful step forward to being recognized.” “Yes, but you’re mixing Greek and Latin. You can’t _do_ that!” [Next page](https://boards.straightdope.com/t/3-is-to-trilogy-as-2-is-to-um/238323.md?page=2)