Near the bottom on the following page http://www.allaboutcircuits.com/vol_1/chpt_10/7.html is the following statement. This is simply wrong. The only requirement for Superposition to be valid is that the system has to be linear. There is nothing nonlinear about the voltages and currents in an unbalanced bridge circuit. If someone believes otherwise, post a (simple, please) example of an unbalanced bridge circuit having only linear components (use resistors to be consistent with this point in the E-Book) that you believe can't be solved with superposition. I'll work it (and, who knows, may learn that I am wrong) and then, either way, it can be added to this portion of the E-Book, either to show how it can be done, or as an example of how it doesn't work. A bit later down the page, it this says this: But since this is shortly after saying: it is in no way "another" prerequisite since components that aren't bilateral aren't linear. Arguably it is redundant and could be removed, but it is probably a useful point to have explicitly made for some readers. This can be patched quite easily by changing it to something like, "Note that the requirement for linearity means that all components must be "bilateral", ...."