ions ▁were ▁al lies ▁of ▁reason , ▁and ▁that ▁they ▁aid ▁in ▁the ▁assim ilation ▁of ▁knowledge . ▁However , ▁Campbell ▁war ned ▁of ▁the ▁m alle ability ▁of ▁em otion ▁and ▁the ▁consequ ent ▁risk ▁in ▁terms ▁of ▁suggest ibility : ▁ ▁[ Em ot ions ] ▁are ▁not ▁supp lan ters ▁of ▁reason , ▁or ▁even ▁riv als ▁in ▁her ▁s way ; ▁they ▁are ▁her ▁hand ma ids , ▁by ▁whose ▁min istry ▁she ▁is ▁enabled ▁to ▁us her ▁truth ▁into ▁the ▁heart , ▁and ▁proc ure ▁it ▁to ▁favor able ▁reception . ▁As ▁hand ma ids , ▁they ▁are ▁li able ▁to ▁be ▁s edu ced ▁by ▁s oph istry ▁in ▁the ▁gar b ▁of ▁reason , ▁and ▁sometimes ▁are ▁made ▁ignor antly ▁to ▁l end ▁their ▁aid ▁in ▁the ▁introduction ▁of ▁false hood . ▁ ▁Draw ing ▁on ▁the ▁social ▁psych ology ▁of ▁his ▁day , ▁propag anda ▁the or ist ▁Edward ▁Bern ays ▁confident ly ▁assert ed ▁that ▁" in ▁certain ▁cases ▁we ▁can ▁effect ▁some ▁change ▁in ▁public ▁opinion ▁with ▁a ▁fair ▁degree ▁of ▁accuracy ▁by ▁operating ▁a ▁certain ▁mechanism , ▁just ▁as ▁a ▁motor ist ▁can ▁reg ulate ▁the ▁speed ▁of ▁his ▁car ▁by ▁manip ulating ▁the ▁flow ▁of ▁gas oline ." ▁ ▁Bern ays ▁ad vised ▁that ▁to ▁change ▁the ▁att itudes ▁of ▁the ▁masses , ▁a ▁propag and ist ▁should ▁target ▁its ▁" imp uls es , ▁hab its ▁and ▁emot ions " ▁ ▁and ▁make ▁" em ot ional ▁curr ents "