And know that there are wonders in the mixing of these principles, for heat and cold are two opposites, so they do not mix, and if they do not mix, there is nothing about them, and likewise humidity and dryness, but the opposite is mixed with the opposite of the other opposite, so only four are ever generated from them, because they are four, and for this reason two are opposites of two, so if it were not If it were like this, the composition of it would be more than what its facts give, and it is not correct for the composition to be more than four principles, for the four are the origins of number, so the three that are in the four with the four are seven, and the two that are in the four with these seven are nine, and the one that is in the four with these nineteen, and add whatever you want after that. You will not find a number that gives you this except four, just as you will not find a complete number except six because it contains half, a sixth, and a third. So heat and dr