▁Par s ons ▁tried ▁to ▁use ▁Fre ud ' s ▁pattern ▁of ▁symbol ization ▁to ▁structure ▁the ▁theory ▁of ▁social ▁system ▁and ▁eventually ▁to ▁cod ify ▁the ▁cy ber net ic ▁hierarchy ▁of ▁the ▁AG IL ▁system ▁within ▁the ▁parameter ▁of ▁a ▁system ▁of ▁symbol ic ▁different iation . ▁His ▁discussion ▁of ▁Fre ud ▁also ▁contains ▁several ▁layers ▁of ▁criticism ▁that ▁reve al ▁that ▁Par s ons ' s ▁use ▁of ▁Fre ud ▁was ▁select ive , ▁rather ▁than ▁orth odox . ▁In ▁particular , ▁he ▁claimed ▁that ▁Fre ud ▁had ▁" int rodu ced ▁an ▁un real ▁separation ▁between ▁the ▁super ego ▁and ▁the ▁e go ". ▁ ▁Sub scri ber ▁to ▁systems ▁theory ▁Par s ons ▁was ▁an ▁early ▁subscri ber ▁to ▁systems ▁theory . ▁He ▁had ▁early ▁been ▁fasc in ated ▁by ▁the ▁writ ings ▁of ▁Walter ▁B . ▁C annon ▁and ▁his ▁concept ▁of ▁home ost asis ▁as ▁well ▁as ▁the ▁writ ings ▁of ▁French ▁phys i ologist ▁Claude ▁Bernard . ▁His ▁interest ▁in ▁systems ▁theory ▁had ▁been ▁further ▁stim ulated ▁by ▁his ▁contract ▁with ▁L J ▁Hend erson . ▁Par s ons ▁called ▁the ▁concept ▁of ▁" system " ▁for ▁an ▁ind isp ens able ▁master ▁concept ▁in ▁the ▁work ▁of ▁building ▁theoretical ▁parad ig ms ▁for ▁social ▁sciences . ▁From ▁ 1 9 5 2 ▁to ▁ 1 9 5 7 , ▁Par s ons ▁participated ▁in ▁an ▁on going ▁Conference ▁on ▁System ▁Theory ▁under ▁the ▁chair mans hip ▁of ▁Roy ▁R . ▁Gr ink er ,