No.. not a stupid question.. honest answer? It's so intuitive to me, that I can no longer remember. But it is standard practice, with many fields but definitely in electronics to write "+ve" for positive and "-ve" for negative, wrt to potentials where "positive" is "a potential which will result in a current flowing in the same direction as conventional current" As I recall. Some of this seeems a bit verbose.. and to be honest it is. In part here is why...
A "Potential Difference" (aka voltage, as far as this conversation is concerned) is exactly that. A difference in potentials. For an analogy, imagine two building, whose rooves are at different heights. The diference is 2 metres. So we have a "height difference" of 2m. Now, as alluded to earlier.. the "potential" to the ground could be a lot more. Let's say both buildings are large and tower around 400m into the air. The "height difference" to the ground is 400m and 402m respectively! We definitely do not want to fall to ground from either.. but we MIGHT want to jump from one to the other. Now, let us define a CONVENTION that travelling from left to right is POSITIVE flow. It turns out that the building on the left is the taller, which means we have to jump left to right (unless we can fly!) so we now have a "height difference" of +2m. If the taller building were on the right, it would be -2m since we would have a difference that OPPOSED our conventional flow model. OK, this 'conventional' bit, what is that about? Well, it turns out that in fact current flows the other way :¬) This is because electrons are NEGATIVELY charged. At the time this was not known and an arbitrary convention was needed. They had a 50/50 chance of being 'correct'... they were not.
Good luck wading through that, and I know it was tangential!
John
edit: corrected a spelling mistake and changed "left" to "right" in second sentence about "jump flow" :¬) Doh!
