Substance term within the context of John Locke's epistemology

John Locke, who is one of the most important representative of Enlightenment Philosophy, made substantial contributions to philosophy via empiricist epistemology. Locke's answers on how human mind works, how, in which ways, and through which sources mind gets the knowledge is the leading of these contributions. Even though Locke is an empiricist, he did not ignore the potential of human mind on producing knowledge, he examined the activity of human mind through reflection, which one of the sources that equips the mind with ideas.Locke is such a philosopher who asserts that the outer world exists independently from perceptions. For this reason, what needs to be done is to put under the scope the process of mind on attaining perception and converting it into knowledge. He handles the essence term also this way within his own system. Locke speaks of the existence of two essence in his philosophy. One of them is the sum of qualities, and the other one is the essence as of the foundation. The notion of these essences is not a priori; on the contrary, he propounds that the essence of the notion we have can be reached through reflection, which is one of the simple idea sources.He asserts that the notion of these essences as all other notions that we have is acquired via reflection. By determining the place of the notion of essence within his system, he asserts that the essence that is the sum of qualities is a necessity for primary and secondary qualities, and for the essence as of the foundation, we have the essences even if it is indistinct, but we cannot indicate its existence implicitly. Key Words: Ideas, Sensation, Essence, Foundation and Qualities.