As we all know, there are three different things in the world. One is the quantity that completely satisfies additivity. Such as mass, the total mass of gas in a container is always equal to the sum of the masses of each gas molecule. For these quantities, 1+ 1=2 is completely true.
The second category is the quantity that only partially satisfies additivity. For example, temperature, if the gases in two containers are combined, the temperature of the combined gases is the weighted average of the respective temperatures of the original gases (this is a generalized "addition"). But there is a problem here: the amount of temperature is not completely additive, because a single molecule has no temperature.