John Locke's essays on human understanding answers the question "What gives rise to ideas in our minds?". In the first book Locke refutes the notion of innate ideas and argues against a number of propositions that rationalists offer as universally accepted truth. In the second book Locke elaborates the role played by sensation, reflection, perception and retention in giving rise to simple ideas. Then he elaborates on how different modes, substances and relations of simple ideas (of the same kind) give rise to complex ideas v.g. space, time, infinity etc. Finally he discusses complex ideas of mixed modes which arise from a combination of simple ideas of different kinds v.g. identity and diversity, cause and effect, etc. (Summary by bala)