The belief that all human knowledge is gained through experience and those aspects of life that cannot be directly experienced must not exist.
As men seek to explain the world around them, and their place within it, new theories are formulated almost weekly and such theory is empiricism. Empiricists believe that the human mind is a tabula rasa (white paper), and our experiences as we grow and learn make a mark on this paper. It is though these marks that we identify with things and understand them.
The work of philosopher John Locke (1632-1704) was the driving force behind the inception of empiricism. He redefined the tabula rasa argument, first worked on by Ibn Tufail in the 12th century. His key works explored the human mind and often clashed with other theorists of his time. The rationalists, for example, held the human mind to be capable of comprehending some things without the need of the senses, through faith. Locke, on the other hand, believed the mind was only capable of comprehending things through experience.
Empiricism is one of the first enlightenment technologies available. It is required for upgrading schools to their next tier, colleges. Under most circumstances, it is also practically required for researching Utilitarianism (which requires a college to be built) and thus opening up the rest of the tech tree. Prussia is an exception to this as they begin the Grand Campaign with a College already built and thus have access to Utilitarianism from the first turn.