In the philosophical sense, empiricists follow the claim that all of our knowledge and concepts are the product of our sensory experience, or that sensory experience is the ultimate source of all of our knowledge and concepts. In comparison, rationalists forward the idea that, while sense experience is part of our knowledge and conceptual construct, that there are significant other resources that operate independently of our sense experience to contribute to our knowledge and concepts.
Both rationalists and empiricists in philosophy operate under the school of epistemology, where the sources, limitations, and nature of our knowledge is the focus of study. Empiricists focus on the multiplicity and significance of all of our sources of concept and knowledge, not just on our sensory experience.
Rationalists use three theses: The Intuition/Deduction thesis; the Innate Knowledge thesis; and the Innate Concept thesis. The requirement for classification as a rationalist is to adopt at least one of these thesis. There is “a priori” knowledge, or knowledge and concept that is innate to us. The external world has knowledge that must be obtained a priori, and that knowledge obtained through our innate reasoning is superior to experience. In some understandings, a priori knowledge includes the knowledge that was given to us at the Creation, is from a previous existence, or came from the process of natural selection.
Philosophical empiricists believe that there is no other source for knowledge or concepts in a subject area but sense experience. This is called “a posterori”, or dependent on sense experience. As such, empiricists reject the theses of rationalists. We have neither innate concepts nor knowledge. Reason does not give us knowledge, let alone superior knowledge. If any knowledge can be gained, the only knowledge that can be gained is by experience.
Amazingly, a person can be a rationalist in some subjects, and an empiricist in others, but can expect disruption in the force when attempting to practice both in the same subject.
In summary, Empiricism is one entity in a competing set of schools which make study of and which have ideas as to how we come to know things. Through empirical knowledge, we emphasise the roles of experience and evidence, with lots of attention to sensory perception to form ideas. The idea of innate knowledge is rejected, with the exception of provable areas, such as genetic predisposition. In empirical science, empiricism is at the heart of the scientific method, where the experiment where all hypothesis and theory must be tested in the real world, rather than relying solely upon a priori reasoning, intuition or revelation.
Stanford Plato “Rationalism vs. Empiricism”