How does science enter policy making, and for what purpose? Surely consulting scientific facts in making policy is done with a view to making policy decisions more reliable, and ultimately more objective. In this paper I address the way/s by which science contributes to achieving objectivity in policy making and social debate, and argue that objectivity is not exhausted by what scientific evidence contributes to either. In policy making and social debates, scientific evidence is taken into account alongside other relevant factors (political, social, economic, ethical, etc.). Such complex contexts of practical interaction constitute a challenge both for the objectivity of scientific evidence (how far should science let extra-scientific facto...