An Essay Concerning Human Understanding is a work by John Locke concerning the foundation of human knowledge and understanding. It first appeared in 1689 with the printed title An Essay Concerning Humane Understanding. He describes the mind at birth as a blank slate filled later through experience. The essay was one of the principal sources of empiricism in modern philosophy, and influenced many enlightenment philosophers, such as David Hume and George Berkeley.

In philosophy, rationalism is the epistemological view that "regards reason as the chief source and test of knowledge" or "any view appealing to reason as a source of knowledge or justification", often in contrast to other possible sources of knowledge such as faith, tradition, or sensory experience. More formally, rationalism is defined as a methodology or a theory "in which the criterion of truth is not sensory but intellectual and deductive".