A young boy is sitting on the grass.
The boy is on the grass.
We don't know if the young boy is The boy.
exists e1 s1 x1 x2.(n_grass(x2) & on(e1,x2) & Actor(e1,x1) & v_sit(e1) & n_boy(x1) & a_young(s1) & Theme(s1,x1))
exists p1 x1 x2.(n_grass(x2) & n_boy(x1) & on(x1,x2))