I assume -tion (as in information, creation, etc.) comes from -tio in Latin, but how did the “n” get in there? Or is this just an unexlpainable philological mystery?
Words ending in -tio end (for example) in -tionis in the genitive case, in -tiones in the N. V. Acc. plural cases, and -tione in the ablative singular. Apart from nominative and vocative singular, the stem ends in -tion.
Generally romance languages seem to have taken the form of the noun from the ablative singular. That’s why the words end in -a, -o, and -tione. We presumably get our nouns from these kinds of romance languages, and not directly from Latin.
We presumably get our nouns from these kinds of romance languages, and not directly from Latin.
Ah, now we’re getting somewhere. My Latin is going ever since I had a job, but I was thinking of verbs morphing into nouns …and then never actually thought about declining them. Is this kind of declension mentioned in Wheelock? I’m skimming through the index and I can’t find an addition of the “n” in any declension examples.
[edit] Nope, I forgot that wheelock doesn’t go into much details with irregular declension patterns.
Wait… then how did “-tio” ended up becoming a noun marker? The “-nd-” for gerunds and gerundives aren’t it. so…?
Is this kind of declension mentioned in Wheelock?
Definitely should be. It’s the third declension.
Definitely should be. It’s the third declension.
No, that’s not what I had in mind. 
I was talking about the patterns of the irregular declensions, like the addition of “s” or “n” that come up often --or semi-often in the world of irregulars.
The endings -io and -tio (-sio), which form actions and abstract nouns from word roots and verb stems, contain an ‘n’ at the end of their stems. All nouns with these endings are of the third declension and it would be unusual and probably confusing for a textbook to tell beginners the reasons for these formations.
You may be interested to read Allen & Greenough’s sections on the third declension. Often through understanding the development of oddities, such as the various forms of third declension nominatives or the third conjugation perfect stems, you may find them easier to remember, less erratic, and maybe even fascinating. The discussion of third declension consonant and i-stems begins in section 53. Your specific question I think is answered in § 61. 1:
- In Masculine and Feminine nouns with liquid and nasal stems (l, n, r) the Nominative is the same as the stem.
Exceptions are the following:- Stems in > on- > drop > n > in the nominative: as in > legio> , stem > legion-> .
The cases from which the Romance languages derive their words varies between the languages and even between the words, but it often coincides with the ablative. I believe the English system (-tio, -ionis > -tion) is modeled after French and is in this case identical the original Latin noun stem. So, to answer your original question, you shouldn’t ask “how did the n get there?”, but “why is the n lost in the nominative?”.
Thank you, my dear Beni! 
why is the n lost in the nominative?
Now that question is going to drive me insane. 
The endings -io and -tio (-sio), which form actions and abstract nouns from word roots and > verb stems> , contain an ‘n’ at the end of their stems.
Ok… so this -tio from verb stems… Gerunds have that -nd- marker; is -tio an older way to form nouns from verbs?
I can’t say which is older but the two different endings have distinct functions. The gerund ending is a part of conjugation, the -tio ending is a suffix. The gerund ending is truly formed from the present tense of the verb and preserves the meaning of the verb (in the active voice). The -tio ending is not a form of the verb, it is merely derived etymologically and historically from the verb to form a related noun. The word with the -tio ending does not always preserve the exact meaning of the verb, being another word altogether free to mutate in sense and idiom; i.e. legere “to read, choose” → legio “a legion”; condere “to found” → conditio “agreement”. The -tio ending is also not formed from any regular part of the verb, as conjugated parts are: laudatio, datio, sponsio, conditio, etc appear to be the supine stem + -io; whereas opinio, optio, etc (as opposed to opinatio, optatio) appear to be formed directly from the root, something which is never seen in conjugation. Finally, the -io ending is sometimes even added to nouns, proving that it is quite a different thing.
You could easily compare it to English with its “conjugation” and suffices. Certainly we would consider the forms “punishing” and “starving” to be conjugated forms of “punish” and “starve”, but would you consider “punishment” or “starvation” to be forms of conjugation? Or would you consider “kingdom” to be a form of the word “king” for that matter? This is similar to the difference between gerunds and abstract nouns. Though textbooks often define the gerund as a “noun formed from the verb” it really is a “verb-noun” as opposed to an abstract noun.
Now this is the kind of explanation that I wish my Latin teacher had more often. Well done. 
I’m done with pestering you (for now), and you can go back to happy meal drive through translations.