Mr moto, I am suggesting that a tail can produce lift becasue it does, but lift doesn't have to be in the positive sense. As has been pointed out, often the incidence of the tailplane on a large aircraft is negative. As it produces some kind of force, it therefore produces a moment about the c of g.
Cuban - I humbly go into reverse over the aerodynamic centre issue, I was just considering a simple case where the tailplane has a positive incidence.
Apologies for any confusion!