Scientists who work to investigate new theories or formulate basic principles are considered to be theoretical scientists.
Scientists are the persons that do research for their lives and are committed to the field of science as their hobby or mode of income. The scientists are many in categories – some like to build new machines or structures that will help in making some processes easier, whereas some of them are interested in investigating new theories and formulating them.
These last type of scientists are called as theoretical scientists. Both of the categories are dependent upon each other as without new theories, new inventions can’t be made. And theories itself can’t do much to progress mankind.