Treaty on the Prohibition of Nuclear Weapons was adopted in 2017. A variety of countrieschose to join, take a position as observers or reject the treaty completely. In this study anexamination of two cases where the country chose to take a position as observers, which isSchweiz and Sweden. The empirical material is two consequence analysis documentspresented by each country. A purpose with this study is to analyze arguments for and againstthe treaty, which is found in the empirical material, to explain why Schweiz and Swedenchose not to join the treaty. This is done in relation to the aspects; humanitarian dimension,security, cooperation and the substantial content of the treaty. Further analysis is based on theinternational relations theories liberalism and realism, which are used as approaches topresent explanations as to why these countries chose to be observers instead of joining thetreaty. The study has shown that a majority of the argument against the treaty is found to bestronger than the argument for joining the treaty, with an exception for arguments about thehumanitarian dimension where the argument for the treaty is stronger. Explanations presentedwith the theoretical approaches result in security playing a big role in the decision, as well asfuture cooperation with other countries based on security and a better possibility to continuedisarmament of nuclear weapons.