Over the years science has developed through a series of discoveries which started off as observed natural phenomena which had to be explained.This was done in a systematic way by using the scientific method which involves three main stages--the hypothesis stage, the theory stage and the scientific law stage.
When a phenomenon is observed, scientist ponders over it and over it and carries out relevant experiments. He sieves through the data and arrives at a possible explanation for the nature of the phenomenon. This explanation, which is still only a trial idea, is known as a hypothesis. It may or may not be proved correct later.
The scientist conveys his hypothesis to the other workers in the same field for discussion and further experimentation. When the hypothesis is supported by a large amount of different types of observations and experiments, it becomes a theory, i.e. a scientifically acceptable idea or principle to explain a phenomenon. A good theory predicts new facts and unravels new relationships between naturally-occuring phenomena.
A theory which is tested and found to fit the facts, and from which valid predictions may be made is then known as a scientific law or principle. However, not all hypotheses and theories pass successfully to become laws. Some may sound very convincing and be supported by mathematical calculations but are very difficult to prove experimentally. This is invariably due to the material under investigation or the lack of suitable working equipment. Sometimes, they are accepted to become laws. A typical example is Avogadro's hypothesis which has not been proved conclusively, and yet is accepted as Avogadro's law.
Science cherishes all forms of ideas and proposals. Even obsolete ideas are kept as reference. Thus, a beginner in science must still learn about Dalton's Atomic Theory even though it has been greatly modified by modern discoveries. It is said that there is no end to knowledge, so developments in science too may have no limits as long as man perpetuates his arduous desire to understand and utilize his immediate environment, and even those seemingly beyond his reach.