Voltage polairty and current direction

The Laws of Circuit - you can learn and practice by just reading

: Degree of Freedom or Sort of
: Circuit problem is eventually asking for or answering two things: voltage and current. Everything else is just a derivative, that is, not new but developed from original.. Then we can say that we have 2 degrees of freedom: voltage and current. So to speak, we can exercise our freedom with constraint. For example, for a resistor in a circuit, we are free to choose the direction of the current OR the polarity of the voltage across the resistor. Hoever, we CANNOT exercise the 2 degrees of freedom AT THE SAME TIME. Because there is the "Passive Convevtion" like the Geneva Convention on treating POWs. In other words, if you choose the direction of the current through a resistor, the polarity of the voltage of the resistor must be set so that the passive convention is satisfied. In a voltage source where the polarity is already set, we have just one freedom of choosing the direction of the current flowing through the voltage source. In a current source case, we can choose only the polarity of the voltage across the current source. In the source case, remember you exercise your freedom, which means, you do not have to follow the passive convention. Sources are NOT passive elements, after all.