▁of ▁the ▁observation ▁itself , ▁rendering ▁limited ▁our ▁ability ▁to ▁identify ▁caus ality . ▁N iels ▁Bo hr , ▁one ▁of ▁the ▁main ▁architect s ▁of ▁quantum ▁theory , ▁suggested , ▁however , ▁that ▁no ▁connection ▁could ▁be ▁made ▁between ▁ind et erm in ism ▁of ▁nature ▁and ▁freedom ▁of ▁will . ▁ ▁Agent / subst ance - ca us al ▁theories ▁Agent / subst ance - ca us al ▁accounts ▁of ▁in compat ibil ist ▁free ▁will ▁rely ▁upon ▁subst ance ▁dual ism ▁in ▁their ▁description ▁of ▁mind . ▁The ▁agent ▁is ▁assumed ▁power ▁to ▁interven e ▁in ▁the ▁physical ▁world . ▁Agent ▁( subst ance )- ca us al ▁accounts ▁have ▁been ▁suggested ▁by ▁both ▁George ▁Ber keley ▁and ▁Thomas ▁Re id . ▁It ▁is ▁required ▁that ▁what ▁the ▁agent ▁causes ▁is ▁not ▁caus ally ▁determined ▁by ▁prior ▁events . ▁It ▁is ▁also ▁required ▁that ▁the ▁agent ' s ▁causing ▁of ▁that ▁event ▁is ▁not ▁caus ally ▁determined ▁by ▁prior ▁events . ▁A ▁number ▁of ▁problems ▁have ▁been ▁identified ▁with ▁this ▁view . ▁First ly , ▁it ▁is ▁difficult ▁to ▁establish ▁the ▁reason ▁for ▁any ▁given ▁choice ▁by ▁the ▁agent , ▁which ▁suggests ▁they ▁may ▁be ▁random ▁or ▁determined ▁by ▁luck ▁( without ▁an ▁underlying ▁basis ▁for ▁the ▁free ▁will ▁decision ). ▁Second ly , ▁it ▁has ▁been ▁question ed ▁whether ▁physical ▁events ▁can ▁be ▁caused ▁by ▁an ▁external ▁subst ance ▁or ▁mind   – ▁a ▁common ▁problem ▁associated ▁with ▁interaction al ist ▁dual ism . ▁ ▁Hard ▁in compat ibil