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A table can have one index, or, it can have two or more [...]?

Is it indexes or indices? I'm just asking since I've noticed they're both used quite often. Even Wikipedia seems to support both variants, although it prefers to use indexes.

Simply put: Which plural is the preferred one?

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migrated from stackoverflow.com Mar 13 '12 at 23:30

This question came from our site for professional and enthusiast programmers.

This page makes a clear distinction: "The plural of the noun index should always be indices. This handily distinguishes it from the present tense of the verb index, which can only be indexes." -federalist.wordpress.com/2006/09/28/grammar-indexes-vs-indices – Chris Ballance Jun 16 '09 at 13:09
Since English is not my native language, I find the checked answer (explaining about plural and noun) just the right answer, so I don't want to uncheck it. Even though both spellings are correct, it's just a good explanation to customers if they ever wonder why I talk about "indices" instead of "indexes". – Wim ten Brink Jun 17 '09 at 7:49
For those coming late to the party, I want to note that from a purely grammatical point of view, this answer is, well, not precisely incorrect, but certainly misleading. It implies consensus where there is none, and says there is only one right answer when there are clearly two. To those who wish to make the English language more logical: we feel your pain, but it just doesn't work that way. – Marthaª Mar 14 '12 at 6:13
@nohat: it's unfortunate that you merged the other question into this one. This one has a bunch of highly-upvoted answers that are not really correct, and the correct answers to the "native" question are lost in the mix. See the meta question about this. – Marthaª Mar 14 '12 at 13:47
@nohat: ah, I see. Stupid undo, it's only ever available when you don't really need it. (I still want an undo that would apply immediately after I drop my favorite porcelain bowl.) – Marthaª Mar 14 '12 at 16:43

From Oxford Dictionaries:

plural of index: indexes or especially in technical use indices

The plural of index is usually spelled indexes, but can also be spelled indices (as in the original Latin) in subjects like science and medicine.

So, technically I'd use indices.

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I like how it specifically mentions technical use. Thanks for the answer. – Jeremy Sep 16 '10 at 21:23
I'm not clear why the jump from "can also be spelled" (which is odd since this is not simply a spelling difference but an actual difference in the word used) to actually preferring "indices". The quote doesn't justify it or even say it is more prevalent. – delete Sep 16 '10 at 22:36
I was taught that books have indexes while maths has indices (similarly, people have appendixes while books have appendices). – TRiG Apr 13 '11 at 23:29
A process that indexes creates indices. The result of that process is an index for each item touched by that process. – JustinC Jun 11 '13 at 8:08
@JustinC: I would say that a process that creates compact identifiers for objects creates indices; a process that creates tables used to find objects creates indexes. – supercat Mar 4 at 16:14

Both are valid English; that is why you see both used. One person may be used to the other, while the guy down the hall says it the other way. See dictionary.com if you haven't already.

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Also in the Oxford Dictionary of English, something like "plural: "indexes" or "indices" (especially in technical writing)". – Richard Jun 16 '09 at 13:24
But I live by myself. – JoeCool Jun 16 '09 at 13:26

One isn't more correct than the other. We speak English, not Latin.

However, if you restrict it to databases, I think the more common spelling is indexes, and Google supports me on this.

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googlefight.com/…; – Nosredna Jun 16 '09 at 13:24
Well quite; but array indices and database indexes are different beasts. I would probably use "array indices", but on the other hand, I would also say "Oracle indexes". – Simon Nickerson Jun 16 '09 at 13:48
Why are array indices and database indexes different beasts? They are both plurals of "index", no? – Lynn Mar 15 '12 at 2:19
Yes, for databases 'indexes' seems to be accepted. In all the Oracle documentation I've read Oracle refers to 'indexes' and I've not ever seen Oracle use 'indices'. – eebbesen Jul 28 '15 at 14:28
I ran several "google fights" and interestingly it showed that "Database Indices" wins over "Database Indexes". HOWEVER, if you do the same comparison except replace "Database" with "Oracle", "Postgresql", "MySQL", or "SQL" the equivalent phrases with "Indexes" beats out those using "Indices" by a huge margin. Perhaps this is indicative of a difference between broad/novice usage vs more specific usage. – Ethan Nov 16 '15 at 23:43

I happen to prefer "indices" but I was wondering if one was generally preferred over the other.

Who are you writing for? That should be the first consideration. For example, opening the Oxford Writers' Dictionary, I find that it tells me to use the plural indexes. So if you're writing for Oxford University Press you'd better use indexes. If you're writing only to please yourself you can use whatever plural you like, so in theory you could be like those people who write unixen and say indexen I suppose, although that might make your writing less popular.

I think indices is common enough that it doesn't come across as at all an eccentric choice.

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This will mostly be used in source code comments or in the code itself. So only other programmers would read it. – Jeremy Sep 16 '10 at 21:24
@Jeremy: in that case, does it help or hurt that a text search for "index" will find "indexes" but miss "indices"? – Mr. Shiny and New 安宇 Sep 17 '10 at 15:09
@Mr. Shiny and New: You make a good point there. Searching for "index" will not find "indicies". However, I am not going to use improper English just to improve searching. I'm not saying that "indices" is improper. But, for example, if I have an object called "mouse", and I want to refer to a group of them, I am going to call the group "mice", not "mouses". – Jeremy Sep 22 '10 at 12:55
@Jeremy: Agree that you should write "mice". But if there was disagreement about which form is best, (and indexes is certainly widely used) and the more useful one should be used, I'd say. – Mr. Shiny and New 安宇 Sep 22 '10 at 13:17

Good question.

I generally feel that "indices" is more correct, but "indexes" more common. So when not trying to be extra highbrow, I uses "indexes".

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Both are valid. I prefer indexes, as it easily convey the meaning.

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The word "index" may be used either to refer to a small piece of information used to identify something else, or to refer to a collection of information used to locate objects when given such an index. I would suggest that the plural of the first form of "index" is "indices"; the plural of the second form is "indexes".

As support for this, see the Merriam Webster entry for index:

plural in·dex·es or in·di·ces

The only definition with further information about the plural form is the fourth:

  1. plural usually indices : a number or symbol or expression (as an exponent) associated with another to indicate a mathematical operation to be performed or to indicate use or position in an arrangement <3 is the index of the expression ∛5 to indicate the cube root of 5>
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Another answer suggests that 'indexes' and 'indices' tend to be used in different contexts, but offers no particular logic as to why. I would suggest that while many people use the plurals interchangeably, the reason "array indices" is more common than "array indexes", but "magazine indexes" is more common than "magazine indices" is that "array index" describes a small token of information while "magazine index" represents a larger collection of information. – supercat Mar 4 at 16:50
@sumelic: As a native English speaker, my first expectation upon hearing the phrase "market indices" would be that it referred to some individual numbers representing market performance. while "market indexes" would refer to directories containing information about market participants, etc. In most cases either meaning could be inferred for either word based upon context, but I think there are times when "indexes" would seem more natural and there are times when "indices" would seem more natural. – supercat Mar 4 at 16:58
@sumelic: Nice edit. Thanks. – supercat Mar 4 at 17:34

Indices seem slightly more common as it is also often used in the formal context (like while working on some project etc.)

COCA (Corpus Of Contemporary American English) also shows that indices is more common. Although both seem to be in widespread use

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I vote "indexes"

Since it's a toss-up, I plan to use "indexes" from now on.

Chris Ballance argues in a comment above that "indices" is easily distinguished from the verb, as in "he indexes things", but I think that would be clear from context.

Meanwhile, "indexes" is a normal-looking plural and "indices" is a weird exception to learn. Languages tend to drop the least-used oddities over time, and I think that's a good thing. Goodness knows we still have plenty of oddities to remember. Think of all the poor toddlers hearing "it's not 'eated', it's 'ate'", and embrace simplifications when you can.

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