here is how my prof taught me : there is a system pi which is connected to a ressistor. we replace the resistor with a current source so the current which flows threw the ressistor did not change and by some other law so does the voltage do not change on that branch. and we replace every intial condition which differs zero with independant source(capacitator which have v(t=0)=5 for example into capacitator v(t=0)=0 and voltage source 5volts) now comes the problematic part "we dissconeect the current source so we have Voc between those two points from system pi,and then we turn every independant source in the pi system into 0 current source gets 0 current (open circuit) voltage source is short circuit. and we get some other voltage coming out of the pi system and so by the super position law we sum them to gether and get thevenin law. question 1: when i hear superposition law i imagine a circuit which has two voltage sources and we dissconnect one of the source and calculate what current flows on some ressitor then we reverse the situation and we calculate again the current and then we sum both currents both half coexyst together. the problem is that in my profs prove there is no two coexysting parts we have once voltage from pi and the other votage from pi when all the intependant sources are zero there is no super postion because those two situations are not on the same time ?? 2.if we turn every initial condition differs zero into independant source then when we turn every source to zero then there is no voltage at all ??