In this paper the lightface Pi^{1}_{1}-Comprehension axiom is shown to be<br />
proof-theoretically strong even over RCA_{0}^{*}, and we calibrate the<br />
proof-theoretic ordinals of weak fragments of the theory ID_{1} of positive<br />
inductive definitions over natural numbers. Conjunctions of negative and<br />
positive formulas in the transfinite induction axiom of ID_{1} are shown to be<br />
weak, and disjunctions are strong. Thus we draw a boundary line between<br />
predicatively reducible and impredicative fragments of ID_{1}.