Development of Numbers 1

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This is a good time to look back briefly at the various types of numbers that we have studied. The history of the development of numbers, from intuitive Natural numbers to abstract Integers and Irrationals, is a good example of the journey from the concrete to the abstract. It is also the story of the development of math from simple ideas to a complex discipline involving abstract ideas &amp; their relations.

Natural Numbers

The quest for numbers started with countable numbers. The numbers which could be related to groups of objects like 1, 5 &amp; 3 etc were called Natural Numbers possibly because they were &ldquo;seen&rdquo; to exist in nature. It was also realized that they were infinite in number and there was no &ldquo;biggest number&rdquo;. These numbers were conceptualized as a set. The numbers 1, 2, 3 and so on formed the Set of Natural Numbers.

The Place Value System was invented to enable any magnitude to be written with just ten numerals. Numerals were symbols which represented numbers. Numbers embodied magnitudes.

The four arithmetic operations on these numbers were invented to model daily activities.

All numbers are abstract

Natural numbers were thought to be &ldquo;real&rdquo;.

All cultures found natural numbers to be useful to keep track of objects &amp; events. But as societies developed, the natural numbers were not sufficient to keep track of objects &amp; events. They had to invent many different kinds of number to meet the needs of the society. It also led to special classes of humans who studied numbers and developed into &ldquo;mathematicians&rdquo;.

Numbers, other than natural numbers, were considered a &ldquo;product of our thinking&rdquo;. The truth is that all numbers, including natural numbers are products of our mind and do not exist in our world in a concrete form.

But even today there are 2 groups among mathematicians – &ldquo;Platonists&rdquo; who believe that numbers exist in the world independently and those who hold that they are just creations of our mind.

Number Labels are Arbitrary

We also need to remember that the names given to different types of numbers - proper/ improper, imaginary & complex are mall just names. They have no mathematical significance. They have no moral or ethical significance. These names, many of which are familiar to us from our daily transactions, have just been given for convenience. This is an important fact that needs to be clarified to students from the lower classes.

Need for new Kinds of Numbers 

While performing these four arithmetic operations with natural numbers, people came across situations where new kinds of numbers had to be invented. Mathematicians invented these new numbers and also formulated rules for operating on them. For this purpose they formulated 2 very important and fundamental concepts.

Idea of Set &amp; Closure
 * 1) Closure Property
 * 2) Fundamental Laws of Arithmetic

Along with the idea of a &ldquo;set&rdquo; of numbers, the idea of &ldquo;closure&rdquo; was formulated.

The idea was that the result of the 4 operations on any 2 numbers from a set, should also belong to the set. That is, a set of numbers should be &ldquo;closed&rdquo; with respect to the 4 operations.

For example, 4 &amp; 6 add to 10. Both 4 ^ 6 and the result 10 belong to the set of natural numbers. Same was true of multiplication. But subtraction and division created numbers which were not natural numbers. Hence such new numbers had to be defined and the natural number set expanded.

Fundamental Laws of Arithmetic

Chapter 21.2 describes the Fundamental Laws of Arithmetic. They consist of 5 properties. At an abstract level, any entity which obeys these laws, is accepted as a number. From another perspective, when any new type of number is invented, the rules of operation are determined so as to be consistent with these laws.

As human cultures invented different kinds of numbers to help them perform more sophisticated tasks, the criterion for accepting the new entities as numbers was to ensure that they obeyed these laws.

This is the mathematical basis of accepting fractions, integers, imaginary numbers &amp; others also as &ldquo;numbers&rdquo; along with Natural numbers.

These laws helped to expand the idea of numbers to represent many areas other than magnitude. One example is that of representing Truth values in logical operations as numbers!

Zero as a number

The idea of &ldquo;Nothing&rdquo; as a number 0 (Zero) was invented as an answer to the question, what is 4 – 4? The rules for applying the four operations to 0 were formalized. But 0 was not part of the Natural Number set.

So the set of Natural numbers was expanded by adding 0 to it and the new set was calledSet of Whole Numbers. Possibly this meant that they can be represented by the presence or absence of discrete objects.

The set of &ldquo;Whole Numbers&rdquo; was &ldquo;closed&rdquo; with respect to both addition &amp; &ldquo;limited cases&rdquo; of subtraction.

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