The verb īnsum has the prefix in-. Prefixing in/in- to words, changes their meaning to ‘in’, ‘on’ et sim., or ‘un-’, ‘non’ et sim. (ɔ:¹ negation).² However, according to Wiktionary, the pronunciation of in changes in some context; this supported by Lewis.

At first, my understanding was that this pronunciation change – ɔ: from [ɪ] to [ĩː] – only occurs where the prefix is not the preposition in, but the actual prefix in-. Even though sounding the same, they have different roots: When meaning ‘in(side)’, it is merely the preposition prefixed; when meaning ‘not’/‘[negation]’, it has the Indo-European origin [*n̥-].5 As it turns out, the pronunciation change is merely a matter of morpheme interaction.

Non of my grammars, however, even the very detailed grammar by Nils Sjöstrand (Gleerups forlag, Malmö/Lund 1960) has any details on these two differences. The only thing I can find that is mildly relevant, is in Sjöstrand § 6.2, explaining the enlonging [I’m sorry, I am not sure what the correct linguistic term is] and nasalisation of vowels in front of ns and nf.


This means that pronunciation alone is not a clue as to whether or not one is dealing with in prefixed, or the prefix in-, as they both will have their pronunciations changed based on which morphemes follow. How can you know whether you are dealing with the preposition or the prefix, and thus the correct meaning of the word?

Somewhat Related


¹ This is not a smiley; it is the symbol meaning ‘that is’, ‘may be read as’ and similar.

² Egil Kraggerud & Bjørg Tosterud: Latinsk ordbok, Cappelen, Oslo 1998: ‘in i sammensetning’.

I have added the negation tag, but am unsure as to its relevance. Advice on this is appreciated. It could very well be that the tag details should be updated to include questions such as this one.

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    I have never seen "ɔ:" meaning "that is" - where did you get it from?
    – varro
    Commented Nov 5, 2018 at 21:52
  • 1
    I grew up with it. My granddad’s old dictionaries, printed in fraktur, were amongst those that often used it, and it is commonly known in stenography. Realising it was not common knowledge, was surprising to me. AFAIK, it was most commonly used in areas influenced by germanic typographical tradition (such as Scandinavia); it seems to be gaining a resurgence now, with more and more people interested in typography and traditions lost. Some links: typografi.org/forklaringstegn/forklaringstegn.html macbasics.wordpress.com/2015/02/22/…
    – Canned Man
    Commented Nov 6, 2018 at 9:56
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    Given that you're writing in English, for an audience familiar with Latin, why not use a convention commonly used in English (for example "i.e.", short for "id est")? Unfortunately, using "ɔ:" is confusing, especially in a site with a linguistics flavour, because readers are far more likely to interpret it as an IPA vowel than your intended meaning - certainly I was confused on my first reading :)
    – psmears
    Commented Nov 6, 2018 at 11:34
  • Two reasons in particular: 1) Realising that the current young students do not have knowledge of it, appears to be a matter of age. 2) Spreading the knowledge. When re-entering uni, I thought it was common knowledge – after all, I had known about it since I was a tiny kid – but soon realised it was not. I assumed this was a matter of age, as people of my own age (in their 30s) were familiar with it. Being that this is a classicist’s site, I assumed this way of spreading knowledge would be appreciated; I hope this was the case.
    – Canned Man
    Commented Nov 7, 2018 at 11:34

2 Answers 2


The negative prefix in- typically attaches to an adjective, while the prepositional prefix in- typically attaches to a verb. The main complication to this distribution is the existence of adjectives derived from verbs (or at least, participle forms that look very similar to adjectives) and nouns derived from adjectives or from verbs. But if you're looking at a finite verb form such as "īnsum", you can be fairly confident that the prefix in- does not express negation.

For either prefix, the vowel is long before ns or nf, and short otherwise. There is no difference in pronunciation between the two prefixes spelled in-. They also share a number of alternative spellings representing assimilated pronunciations, such as im- ir- il-, which likewise are pronounced the same for both prefixes regardless of the meaning. (Many words can take either an assimilated or unassimilated spelling, as discussed at -NL- and -LL- in Classical Latin ; I'm not sure whether the rates of assimilated spellings differ between the two prefixes.) The negative prefix has a rare form ig- that I don't think occurs as a form of the prepositional prefix.

Finite verbs are very rarely negated with in-

"Prefix Derivation in Latin", by Dana DINU, says that the negative prefix in- "does not apply to verbs".

This is almost always true. (There are slightly more exceptions than I would have guessed). So far, I've found only the following possible exceptions, some or all of which may actually be back-formed from related adjectives (rather than derived from affixing in- directly to the verb):

  • ignōscō, "pardon, forgive", is explained in some sources as coming from the negative prefix and (g)nōscō. For example, Lewis and Short says "lit., not to wish to know, not to search into; hence, with esp. reference to a fault or crime, to pardon". I have asked a separate question about ignōscō to try to determine the explanation for this unusual case.

  • improbō, "disapprove, condemn". I'm guessing it is a backformation from improbātus < in- + probātus.

  • indecet, "be indecent, unseemly", mentioned by Knapp (1917) when discussing ignosco. Looks like a likely backformation from indecēns. This verb seems to be extremely rare.

  • inobaudiō/inoboediō, "disobey". I'm guessing it is a backformation from inobaudiens/oediens. Seems rather rare.

    Example: Tertullian's Adversus Marcionem:

    Cum ergo mandato diceret populo, Ecce ego mitto angelum meum ante faciem tuam, qui te custodiat in via et introducat in terram quam paravi tibi, intende illi et exaudi eum, ne inobaudieris eum; non enim celabit te, quoniam nomen meum super illum est

Participle forms can often be negated with in-, but possibly only when they are actually participial adjectives

Here is a quote I found that indicates that in Classical Latin, non was used to negate verbal participles, while in- appears as a negative prefix for participial adjectives. (If you don't understand what those terms mean, it might help to look at my question about how these two categories of participial forms were distinguished in Latin.)

in Classical Latin the synchronic negative of e.g. patiens ‘enduring’ is non patiens, whereas participles with a negative prefix are synchronically non-participial adjectives, e.g. impatiens ‘impatient’.

(p. 30, "Negated Participles in Rgvedic Sanskrit and Proto-Indo-European," by John J. Lowe, Indo-Iranian Journal 54 (2011) 19-38)

If this rule is true, it would make the distribution of non and in- negation in Latin closely analogous to the distribution of not and un- negation in English for participial forms.

Since participle forms can also contain the prepositional prefix in-, there are some cases of ambiguity between the two in- prefixes.

  • This is a very interesting answer. Given this be true, you could in fact with some a priori knowledge – as you explain: is the latter part of the word a verb or adjective – tell whether we are dealing with in- or in. Do you have any sources?
    – Canned Man
    Commented Nov 6, 2018 at 9:59
  • With regards to knowing what you are dealing with by pronunciation, I specifically mention this is not possible in the question.
    – Canned Man
    Commented Nov 6, 2018 at 10:01
  • Ah, thanks. I will have a read and try to correct my phrasing. The question was rewritten a couple of times.
    – Canned Man
    Commented Nov 6, 2018 at 10:33
  • I have updated my question to reflect that which is stated under the questions heading. I apologise for inconsistency.
    – Canned Man
    Commented Nov 6, 2018 at 10:58
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    @sumelic: e.g., cf. the contrast in English between these two adjectival passives: "*The letter was unwritten by Mary" vs. (?) "The letter remained unwritten by the lawyers" (NB: the latter drawn from [http: //academia.edu/1368590/Syntactic_affixation] ). I was wondering why the latter sounds better (though perhaps a bit dubious) compared to the former, which sounds awful. What about "This question remains uncontested by any scholar in the field"? I'm not a native speaker of English but it sounds ok to me.
    – Mitomino
    Commented Aug 19, 2019 at 3:57

I don't think it's possible to distinguish in meaning "in" from PIE *en and in- meaning "not" from PIE *n̥ from pronunciation alone. It's well known that the /i/ in in- lengthens when followed by certain consonsant combinations such as "ns" and "nf", but as far as I know, that is purely phonetically determined and has nothing to do with the ancestral morpheme.

So, basically, there is no a priori way of distinguishing the two cases.

  • The vowel lengthening is supported by multiple grammars (e.g. Sjöstrand § 6.2.2), so I agree with you on that. But I would find it surprising if there are no grammarians who ever commented on this seeming (unless having knowledge of PIE, which they didn’t) incongruency. Could there perhaps be anything to gather from ancient sources? Your answer still deserves upvotes, for noting the lengthening in front of ns and nf, which learned about after reading your answer.
    – Canned Man
    Commented Nov 5, 2018 at 21:54
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    @CannedMan: what incongruency are you referring to? That the I in in can be short in some phonetic environments and long in others?
    – varro
    Commented Nov 5, 2018 at 22:05
  • The inconsistency I am talking about, is the (theoretical?) possibility of words that are both homographs and homophones having different meanings. One could for instances think of a word such as inesse existing in two forms, both written and pronounced the same way, but one meaning ‘be in’ and the other ‘un-be’, ɔ: either ‘not to be’ or ‘cause to cease to exist’.
    – Canned Man
    Commented Nov 6, 2018 at 11:03

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