How can we explain that small states are able to influence decisions over the EU's external policy? The aim of this article is to explain why small states are able to influence decisions in the EU's foreign and security policy with a detailed analysis of the Swedish-Finnish initiative on including crisis management in the Amsterdam Treaty in 1997. The article investigates the explanatory power of two hypotheses derived respectively from the assumptions of an intergovernmentalist and a deliberative approach. The empirical material shows that inclusion of the Petersberg tasks can neither be assessed by exclusive reference to the cost - benefit calculation of the fixed interests to France, Germany and the UK, nor with reference to intense preferences for Sweden and Finland or possible threats of veto. There is a better fit between the empirical data and the expectations derived from the deliberative perspective. In cases of small state influence in the EU's external policy, we therefore need to test the possibility of arguing as a mode of interaction.