<P> In response to the early - to - mid-17th century "continental rationalism" John Locke (1632--1704) proposed in An Essay Concerning Human Understanding (1689) a very influential view wherein the only knowledge humans can have is a posteriori, i.e., based upon experience . Locke is famously attributed with holding the proposition that the human mind is a tabula rasa, a "blank tablet", in Locke's words "white paper", on which the experiences derived from sense impressions as a person's life proceeds are written . There are two sources of our ideas: sensation and reflection . In both cases, a distinction is made between simple and complex ideas . The former are unanalysable, and are broken down into primary and secondary qualities . Primary qualities are essential for the object in question to be what it is . Without specific primary qualities, an object would not be what it is . For example, an apple is an apple because of the arrangement of its atomic structure . If an apple was structured differently, it would cease to be an apple . Secondary qualities are the sensory information we can perceive from its primary qualities . For example, an apple can be perceived in various colours, sizes, and textures but it is still identified as an apple . Therefore, its primary qualities dictate what the object essentially is, while its secondary qualities define its attributes . Complex ideas combine simple ones, and divide into substances, modes, and relations . According to Locke, our knowledge of things is a perception of ideas that are in accordance or discordance with each other, which is very different from the quest for certainty of Descartes . </P> <P> A generation later, the Irish Anglican bishop, George Berkeley (1685--1753), determined that Locke's view immediately opened a door that would lead to eventual atheism . In response to Locke, he put forth in his Treatise Concerning the Principles of Human Knowledge (1710) an important challenge to empiricism in which things only exist either as a result of their being perceived, or by virtue of the fact that they are an entity doing the perceiving . (For Berkeley, God fills in for humans by doing the perceiving whenever humans are not around to do it .) In his text Alciphron, Berkeley maintained that any order humans may see in nature is the language or handwriting of God . Berkeley's approach to empiricism would later come to be called subjective idealism . </P> <P> The Scottish philosopher David Hume (1711--1776) responded to Berkeley's criticisms of Locke, as well as other differences between early modern philosophers, and moved empiricism to a new level of skepticism . Hume argued in keeping with the empiricist view that all knowledge derives from sense experience, but he accepted that this has implications not normally acceptable to philosophers . He wrote for example, "Locke divides all arguments into demonstrative and probable . On this view, we must say that it is only probable that all men must die or that the sun will rise to - morrow, because neither of these can be demonstrated . But to conform our language more to common use, we ought to divide arguments into demonstrations, proofs, and probabilities--by' proofs' meaning arguments from experience that leave no room for doubt or opposition ." And, </P> <P> "I believe the most general and most popular explication of this matter, is to say (See Mr. Locke, chapter of power .), that finding from experience, that there are several new productions in matter, such as the motions and variations of body, and concluding that there must somewhere be a power capable of producing them, we arrive at last by this reasoning at the idea of power and efficacy . But to be convinced that this explication is more popular than philosophical, we need but reflect on two very obvious principles . First, That reason alone can never give rise to any original idea, and secondly, that reason, as distinguished from experience, can never make us conclude, that a cause or productive quality is absolutely requisite to every beginning of existence . Both these considerations have been sufficiently explained: and therefore shall not at present be any farther insisted on ." </P>

If you find from your own experience that something is a fact