John Locke was a 17th century empirical philosopher. In his work An Essay concerning Human Understanding, he set out to examine the sources of human knowledge, and to what degree of certainty these sources of knowledge were ultimately capable of achieving.
             Like Descartes before him, he was concerned about the validity of present human knowledge, but unlike Descartes, he did not seek absolute epistemological and metaphysical certainty. He was prepared to accept the fact that some knowledge or understanding was beyond human comprehension.
             Locke begins his essay in Book 1 by arguing against the concept of innate ideas. Empiricists such as Locke claim that nothing can come a priori or prior to experience. Locke believed the mind at birth was like a tableau Rasa or blank slate, which experience can then make its mark.
             In chapter one, of Book one, Locke tackles the most favorable argument for innate ideas, the evidence of "universal consent". This argument states that all cultures have common ideas concerning such things as fire, heat, and numbers. However, Locke counters this argument with "Universal consent proves nothing innate". Locke explains that these ideas are universal not because they are innate, but because they are common to all human experience. Locke also points out that it is evident that some children and mentally handicapped persons do not automatically have ideas naturally imprinted on them at birth.
             According to Locke all ideas originate from one of two different sources, either sensation or reflection. Sensation is the greatest source of our ideas; they come from our sensations of external objects into the mind, producing ideas of such things as hot, cold, hard, and soft. Reflection is the mind reflecting or understanding within itself. This category includes such mental task as thinking, doubting, reasoning, and willing.
             For Locke all ideas are classified as either simple or complex....