Anything which occupies space and has mass is matter. All solids, liquids and gases around us are made of matter. Scientist believe that matter is made of tiny particles that clump together. You cannot see these particles but you can see the matter, for example, a book, a car, a letter, a hand set, a piece of wood, tree, a bag.
Matter has mass means matter has weight: the heavier an object, the more mass it has. Matter occupies space it means matter has volume.
A substance is a pure kind of matter having only one kind of constituent particle (atom or molecule). Water, iron, gold, copper, aluminum and oxygen are examples of substances. All substances are matter but all forms of matter are not substances.
Human beings have been questioning the nature of matter. In ancient times there were two different views about it. One school of thought believed that if we take a piece of matter (for example stone) and break it into smaller pieces and break these smaller pieces into still smaller pieces, the process can be repeated any number of times. This would happen because matter is continuous and its piece of any size can be broken or subdivided into smaller pieces. Greek philosophers Plato and Aristotle belong to this school of thought.
The second school of thought believed that process of subdivision of matter can be repeated only for limited number of times. A stage would be reached when the tiny particles of matter so obtained cannot be further subdivided. They believed that all matter is composed of very tiny particles. In other words, the matter has particulate nature. The smallest indivisible particles of matter were given the name "atom" from the Greek word "atomos" for "indivisible". Indian philosopher Kanada and Greek philosophers Leucippus and Democritus belong to this school of thought.
The term "atom" was coined by Democritus. Today the idea of atom has changed since it was first proposed. The modern idea of atom originated with John Dalton in 1803. Today we talk of two types of constituent particles - atoms and molecules. Atoms is a basic unit of matter and all chemical properties of matter can be explained on its basis.
Matter can be classified in many ways. However, the following are the two main ways of classifying the matter:
By the physical state of matter as a solid, liquid, or gas
By the chemical composition of matter as an element, compound or mixture.