But the Tortoise grants (C), and resumes his skepticism, asking how he can be logically forced to accept (Z) when he accepts (A), (B), and (C).  It soon dawns on Achilles that the mere addition of further premises (like “If (A), (B), and (C) are true, (Z) must be true”, and so on) won’t help resolve the Tortoise’s skepticism. One could keep on adding such premises ad infinitum and yet not get the Tortoise to accept (Z).