Using science, making policy: what should we worry about?

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 factors interfere with scientific facts, without endangering the objectivity of evidence?), and for the objectivity of the role of the scientist in the policy-making process (is he/she only to inform policy, and only on matters of scientific evidence? Or should they also ultimately advise on what to do, running the risk of becoming partial on matters of evidence?) I analyse a case study - the ongoing debate over the spread of bovine TB in the UK - that displays some of the worries and several of the aspects we ought to keep in mind when we bring scientific objectivity to bear on social debate and policy making. I argue in favour of a picture where scientific objectivity enters a productive and effective dialogue with practical objectivity.