Ramsey's theorem for n-tuples and k-colors (RT n k) asserts that every k-coloring of [N] n admits an infinite monochromatic subset. We study the proof-theoretic strength of Ramsey's theorem for pairs and two colors, namely, the set of its Π 0 1 consequences, and show that RT 2 2 is Π 0 3 conservative over IΣ 0 1. This strengthens the proof of Chong, Slaman and Yang that RT 2 2 does not imply IΣ 0 2 , and shows that RT 2 2 is finitistically reducible, in the sense of Simpson's partial realization of Hilbert's Program. Moreover, we develop general tools to simplify the proofs of Π 0 3-conservation theorems.