Okay, this might be a weird question and I am not sure which sub-forum it belongs to - Math, biology or here. We have this concept of more or less. Given two quantities, we can see whether they are equal, more or less. So we assign each quantity some number, symbol to address it. Similarly with emotions like love, hatred we can say whether somebody love the person more or less compared to other. Although it's subjective, we have this more or less concept for emotions too.