  Of particular interest with regard to the question of pluralism are those points along the well-founded sequence that correspond to certain limitative conceptions of the nature of mathematics, such as the degree marked by Q (Robinson Arithmetic, which corresponds to strict finitism in the sense articulated by Nelson), the degree marked by PRA (Primitive Recursive Arithmetic, which corresponds to finitism in the sense articulated by Tait), and the degree marked by ATR0 (Arithmetical Transfinite Recursion, which corresponds to predicativism in the sense articulated by Feferman). In each case, one draws the line at a certain point in the hierarchy, maintaining non-pluralism below and pluralism above. 