John Locke is one of the most influential philosophers in history. Following in the British empiricists' tradition, his works are dominated by logic and a rigid straight-forward language. He was recognized as a great personality during his lifetime, and in 1668 he was elected 'Fellow of the Royal Society'.
In his main work, Locke desired to examine man's cognitive faculties, and because of this he is considered the founder of the critical orientation in philosophy. Basically, he wanted to discover and decipher the origin, extent, and certainty of human knowledge. He stated the theory that at birth the human mind is similar to a white piece of paper on which nothing is written, and therefore the mind gains a multitude of ideas from experience. In other words, all of our knowledge in the final analysis comes from and rests on experience.
Simple ideas are born from experience through the faculty of perception, which has two different parts: sensation and reflection. Through sensation we gain the information given by our senses concerning exterior things, and turn them into simple ideas about their material qualities. Ideas can originate from only one sense or by the collaboration of more than one. Therefore, knowledge that we obtain in this matter requires a direct interaction between senses and external objects. In the absence of the object, we cannot form an idea about its qualities, and the other way round, in the absence of the sense organ the subject cannot form the corresponding ideas.
Reflection consists in the perception of the internal processes of our own mind when it concentrates on the ideas that we gained. In this way, new categories of simple ideas are born: faith, will, etc. This means that the principle ideas that we gain in intellect and from the object that impersonate our senses are cognitive processes. Reflection is similar to sensation, because it is an aspect of the same faculty (the faculty of perception) and can also be named internal sense, because it is a form of the intellect's perception of itself. In order to become a part of knowledge, the sensation datum must be processed by the intellect, which means that between sensation and perception there is unity. The ideas of unity, of power, succession, existence, and pain are acquired both ways. To have ideas and to perceive is basically the same thing.
By founding knowledge on experience, John Locke puts forward an empiric point of view. As a result, he considers information as dependent on external objects and reflection as inevitably linked with sensation.
Locke also believes that complex ideas are composed from simple ideas, only that he forcefully underlines this fact. According to him, there is no reason for us to believe that the soul thinks before the senses give it the ideas upon which it can meditate. Therefore, he undermines and minimizes the creative capacity of the intellect. The abstract ideas of reason do not add anything to the body of knowledge as opposed to the simple ideas of sensation. However, he admits that the mind is more active than perception and that it can compose in its own way complex ideas by the method of abstraction and comparing and combining simple ideas.
Locke is a critic of the Innate Ideas Theory (theory stating that some or all ideas are inborn) which he considers a doctrine promoted by scholastics and theology. He rejects it because he considers it dogmatic. Through its social function this theory makes people credulous and easy to govern.
In the same manner in which he rejects innate ideas, he also cannot accept the existence of immutable principles. He only admits as inborn the faculties that make gaining knowledge possible, and not their results. Cognitive faculties are natural and the rules they elaborate are positive, which means they are gained by man and promoted by society. In this sense, he uses two arguments. First, complex ideas can be innate only if simple ideas are also innate, because the product cannot be previous to the parts. Second, simple ideas are not innate unless they have a universal character. However, experience shows us that innate ideas do not exist in children, idiots, and wild people.