What do we mean by Numbers? A simple introduction to Set Theory
The vast majority of people never think about what they mean when they use numbers to describe things. The concept is so ingrained into our early development that we simply take for granted the fact that people understand us when we apply numbers to different things. For most people, numbers are simply numbers, and questions about the meaning of those numbers are confusing and seemingly nonsensical.
Mathematicians are not most people.
For quite a long time, now, mathematicians have recognized that there are at least two very distinct ways in which we use numbers to describe things. Being the scholarly, academic types that they are, mathematicians have assigned names to these two different types of numbers which sound heady and difficult to the average person: ordinal numbers and cardinal numbers. Indeed, even mathematics students sometimes need quite a bit of work and explanation in order to really grasp the difference between these two types of number; but I’m going to do my best to explain these things in a very simple way for a casual audience.
Ordinal and cardinal numbers roughly correspond to the ideas of value and size, respectively.
Boxing Pythagoras 