The dispute between rationalism and empiricism concerns the extent to which we are dependent upon sense experience in our effort to gain knowledge. Rationalists argue that there are significant ways in which our concepts and knowledge are gained independently of sense experience. They tend to think that some ideas, such as the idea of God, are innate. Empiricists argue that sense experience is the ultimate source of all our concepts and knowledge, and there are no inborn ideas.
Rationalists adopted three arguments:
1. The Intuition/Deduction Thesis: Some propositions in a particular subject area are knowable by us by intuition alone. Still others are knowable by being deduced from intuited propositions.
2. The Innate Knowledge Thesis: We have knowledge of some truths in a particular subject area as part of our rational nature.
3. The Innate Concept Thesis: We have some of the concepts we employ in a particular subject area as part of our rational nature.
René Descartes (1596-1650) divided ideas into three categories:
1. Adventitious ideas are perceived by the senses, such as the idea of the sun being yellow, bright and round. They cannot be manipulated or changed by the mind. For example, a person stands in a cold room, and he/she can only think of the feeling as cold and nothing else.
2. Factitious ideas are gained by everything we find out about an idea, the perception about an object we construct in our minds. For example that the sun, constructed by astronomical reasoning is a vast, gaseous body. These ideas are fabricated and invented made by the mind. For example, a person has never eaten moose, but assumes it tastes like cow.
3. Innate ideas are "true, immutable, and eternal essences," like God, the mind and mathematical truths. The existence and perception of a triangle, for example, is independent from what we can learn about it. So, the features of a shape can be examined and set aside, but its content can never be manipulated to cause it not to be a three sided object. These ideas are made by God in a person's mind.
Gottfried Wilhelm Leibniz (1646-1716) believed that all ideas are innate. He said that "each substance is a world apart" and that "monads have no windows," meaning nothing actually comes from sensory experience. Leibniz divides things into ideas, which exist in the soul whether we actually perceived them or not, and thoughts, ideas we form or conceive at any given time. Ideas dispose us to have certain thoughts on the occasion of certain experiences.
John Locke (1932-1704) could not accept that the mind can have ideas without being aware of them. He believed that the human mind is a tabula rasa (blank tablet) at birth, on which the experienced derived from sense impressions as a person's life proceeds are written. He thought there are two sources of our ideas: sensation, which is not subject to analysis, and reflection.
David Hume (1711-1776) also believed that all knowledge comes from sense experience. He divided all human knowledge into two categories: relations of ideas (mathematical and logical propositions) and matters of fact (propositions involving some contingent observation of the world. All ideas derived from "impressions," which correspond to sensations. To remember or to imagine such impressions is to have an "idea," so ideas are the faint copies of sensations.
A priori principle supports the idea that the world is intelligible. Leibniz argued that everything happens in an orderly, lawful, rational manner, and the mind is able to reproduce the interconnections of things in thought, provided it adheres to certain rules of right reasoning. Locke responded that the only knowledge humans can have is a posteriori, i.e. based on experience.