In a recent SE answer I've written:
I think that other answerers can address this with more historical thoroughty than I, so I'll defer to their expertise, but it sounds like the LRO frozen orbit is likely the best representative example of what's been achieved to date.
I'd hoped that it would turn out to be a word, and it's possible that others have in the past as well
Google Ngram viewer shows usage of the word surfacing around the beginning of the nineteenth century and reaching a minuscule crescendo around the beginning of the twentieth century before dropping into the noise soon after.
though comments suggest this represents the rate of typographical errors.
To me it seems that while thoroughty had the chance to exist in the English language, somehow thoroughness always had the upper hand and finally won.
Question: Are there any grammatical or historical reasons why thoroughty could not have functioned just as well as thoroughness? Is there a general trend or rule when -ty and -ness are both possible, or has it been essentially random? Are there any cases where they coexist?
The English Lessons Brighton article How to use suffixes to create nouns from adjectives and verbs lists -ness and -ity but not -ty (except in comments) but I don't see any discussion as to how these selections arose.
I'm thinking of uses such as
- proceed with all due thoroughty/thoroughness
- they demonstrated exemplary thoroughty/thoroughness