AbstractThe Green function approach to the Heisenberg ferromagnet is confronted with the difficulties connected with the commutation rules of spin operators. Recently, Baryakhtar, Krivoruchko, and Yablonskii (BKY) proposed a new diagram technique for Green functions containing spin operators based on the corresponding technique by Izyumov and Kassan‐Ogly. The new approach is compared with that proposed earlier by Haberlandt and Kühnel. Calculating some crucial terms it is shown why the diagrams of BKY do not represent the corresponding analytical terms properly if kinematic interaction due to the peculiar commutation relations is involved. The results for the low temperature spin wave energy and magnetization are discuss