A man holding an unknown blue object sitting on the ground in a black shirt.
the object is a vase
Just because there is an unknown blue object doesn't mean it is a vase.
exists e2 e1 s1 s2 s3 x1 x2 x3 x4 x5 x6.(n_ground(x5) & a_topic(x1) & Theme(e2,x3) & Actor(e2,x2) & v_hold(e2) & on(e1,x5) & in(x5,x6) & n_shirt(x6) & a_black(s3) & Theme(s3,x6) & Actor(e1,x4) & v_sit(e1) & (x3 = x4) & n_object(x3) & a_blue(s2) & Theme(s2,x3) & a_unknown(s1) & Theme(s1,x3) & (x1 = x2) & n_man(x1))
exists p1 x1.(n_object(x1) & exists x2.((x1 = x2) & n_vase(x2)))