Is there a common (not too formal) specific word or expression used to state that someone is doing something with a hidden, but not necessarily bad, purpose?
I mean something analogous to the Italian expression avere secondi fini.
Searching the net I've found two of them:
- to have ulterior motives
- to have a hidden agenda
The first seems fairly formal (I've never heard that until today), whereas I wouldn't use the second for small matters. A government or a manager could have an hidden agenda, but could we say that a 14 years old has an hidden agenda (not ironically, of course) if he asks his mom if he can help her washing the dishes?
Are my conclusions/impressions in the previous paragraph correct? Are there alternative expressions besides those two?
I'm looking for common, informal, idioms, but not slang, i.e. something that can be also acceptable in a written text, albeit informal.