ADJ on n
The 'keen' group
These adjectives indicate that someone likes someone or something very much. We include here hooked, which indicates that someone is addicted to a drug, and fixated, which indicates that someone is obsessed with something. We also include the adjectives hell-bent and intent, which indicate that someone is determined to do something.
I'm not that big on religion.
We would not be fixated on one person to the exclusion of the world.
He asked about you. I think he's still sweet on you.
In the case of fixated, hooked, keen, and stuck, the preposition on is sometimes followed by an '-ing' clause. In the case of hell-bent and intent, the preposition is usually followed by an '-ing' clause.
He's always very intent on doing what he wants.
In the case of keen, the preposition on is sometimes followed by a noun group and an '-ing' clause. This pattern is ADJ on n -ing.
I don't think my dad's too keen on me going away.
The adjective intent is sometimes followed by upon instead of on.
big fixated hell-bent hooked intent keen mad stuck sweet
Her husband was intent upon maximizing production in the fields.