How to interpret a state treaty

The state treaty (fi) between Russia and Finland has been in the news lately. First constitutional scholars, Professors Ilkka Saraviita and Lauri Hannikainen, said (fi) that it might stand in the way Finland from joining NATO. Russian expert Dmitri Trenin of the Moscow Carnegie Center opined (fi) that Russia would interpret a move to join NATO as being in violation of the letter and the spirit of the treaty. Trenin believes that the treaty will be renegotiated at some point. The root of the trouble is the treaty's fourth article, which states that "the contracting parties will not use and will not allow their territories to be used in an armed attack against the other contracting party" (my translation).

Prime Minister Matti Vanhanen disagrees and so does Foreign Minister Ilkka Kanerva. I think they are correct in practice when they argue that the treaty wouldn't stop Finland from joining NATO. Nevertheless, I wouldn't bet against them wanting to renegotiate the treaty when it's up for renewal in 2012, like Trenin suggests will happen.