Difference between Invention and Discovery
When a person says that he has invented something, it means that he has made or created something that did not have any existence previously. In short the particular thing owes its existence solely to its inventor. On the other hand, a person is said to have discovered something, when he/she finds something that already existed in this world, but its existence was not known before the moment of its discovery. But invention and discovery do have a relation between them. There are many instances where people end up inventing new things based on the principles that were discovered long back. However the vice versa may not hold true in all cases, but that does not mean that it may not be true at all.
Let us take the example of science in order to explain the difference between invention and discovery. Alexander Graham Bell was the scientist who INVENTED the first practical telephone. On the other hand, Watson and Crick DISCOVERED the Double helix structure of DNA. Telephone was something that did not previously existed before its invention, but the structure of DNA was something that existed in all living beings since the beginning of life.
Inventing something requires a lot of planning, calculations and a lot of unsuccessful pre-products, formed as a result of Trial and error. It is a pure and original work of the brain of the inventor. On the other hand, discovery does not involve that much of efforts, but it happens when the discoverer comes across it with the intention of finding it. We cannot regard an invention as a mere accident, neither can a discovery be purely regarded as an accident. Exploration is an important ingredient of discovery which is not the same for invention. Discovery of anything is made public so as to make the people accustomed with the minute details and concepts of the discovery. For example, if the discovery of INDIA by Vasco De Gama was not made public, people would not have come to know about the existence of a country called INDIA.
In short, discovery and invention are neither totally dependent, nor totally independent of each other. Rather, discovery maybe regarded as a subset of invention. Invention is a result of so many failed and partially successful experiments of an individual, whereas discovery is the result of determination as well as strong will of n individual.
In short, invention can be regarded as a scientific process, while discovery is all about nature and its surroundings.