A dog chews on a stick.
A dog has no toys.
Just because the dog chews the stick doesn't mean that it is doing so because it has no toys.
exists e1 x1 x2.(on(e1,x2) & n_stick(x2) & Actor(e1,x1) & v_chew(e1) & n_dog(x1))
exists x1.(-exists e1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_have(e1) & n_toy(x2)) & n_dog(x1))