Geoff wrote:Both "Tongue" and "Cause" are singular and feminine. The article before tongue marks it as the subject. This demands that "cause" is the predicate nominative since they must agree. That leaves us with two modifiers.
Agreed. Further supported by lack of article before the predicate nominative.
Geoff wrote:Correct me if I'm wrong, but these shouldn't be thought of as substantive except in the abscence of appropriate nouns.
Agreed. If they were substantive adjectives, you would also expect them to have an article.
Geoff wrote:There are no conjunctions so you're not looking at multiple clauses. (i.e. the tongue is of "the" many and is a cause of evils).
Agreed.
Geoff wrote:A noun with a modifier where both have no article is common, acceptable and can be either attributive or substantive, but context must tell which it is, att. or sub.
Not quite sure of your meaning. An anarthrous noun+adjective typically functions as a substantive in the predicate - our case. Did you mean "
predicative or substantive" rather than "attributive or substantive"?
Geoff wrote:Since this is acceptable "evils" goes with "cause" and the concord with "many" links it together with the "evils".
Agreed.
Geoff wrote:The thing that makes this sentence tricky is the non-agreement in number with the feminine nouns (You could expect this behaviour from Neuters).
Not sure what you mean. There is no disagreement between the two feminine nouns. Do you mean between the singular nouns and the plural genitives?
Geoff wrote:The thing I want to know is whether this is an actual quote from a text or if it is made up.
I too would like to know this.
Geoff wrote:Finally, someone with real greek knowledge please comment on my post and let me know if there are any mistakes or overgeneralizations or anything, I don't take offense. I'm just trying to learn.
I do not have 'real greek knowledge'. I'm just making it up as I go along.

That said, your analysis seems solid to me.
Cordially,
Paul