Dative of Service

[massimo.p]

Allen and Greenough give the following examples of the Dative of Service:

1). Cōgis mē dīcere inimīcum Frūgī.(Font. 39)
You compel me to call my enemy Honest.

2). hominēs satis fortēs et plānē frūgī (Verr. 3.67)
men brave enough and thoroughly honest
[Cf. Erō frūgī bonae. (Plaut. Pseud. 468) I will be good for something.

I am at somewhat of a loss understanding these translations as either "that for which a thing serves" or "that which it accomplishes," (as A&G say) and the selective use of the word "frugi."

Can someone help with a brief explanation?

 

[Glabrigausapes]

I'm sometimes a little surprised at how abstruse A&G can be. In my opinion, there is no need for this category at all. It's not as though any old word can play this role; one can't really say ero soli 'I will be for the sun.'

They merely want to illustrate that some few nouns (there are others, I think, but I'm afraid I can't think of any) may be used predicatively, like adjectives, in the dative. This dative is really the same 'dative of purpose/result/role/whatever' that makes up the latter part of the so-called double dative construction.
Misit pecuniam mihi frugi. 'He sent me money unto some (good) end/to be of service.'

I reckon the English phrase 'of service', which functions in much the same way, had some influence on their classifying what is really just an idiom as its own unique use of the dative.

 

[massimo.p]

Thank you so much!