No, it cannot be arbitrary at all. (in this answer I will use the words “plus” and “minus” instead of “positive” and “negative”) “Plus” is the effect towards outside (expansion, blowing, explosion), “Minus” is the effect towards inside (contraction, suctioning, implosion). For example, the act of inhaling is plus, because our chest expands; the act of exhaling is minus, because it reduces in size. From the history of electromagnetism it is known that Benjamin Franklin (1705-1790) is the man who was the first to introduce the terms “positive” and “negative”, i.e. “plus/minus” in the field o