In epistemology, philosophers examine the nature, origins, and limits of knowledge. The questions raised in epistemology are:

• How can one gain knowledge?
• What are the limits of knowledge?
• What is the nature of true knowledge?
• What warrants it to be true?

In answering the first question about how knowledge originates, there are two contrasting theories in philosophy: empiricism and rationalism.

EMPIRICISM

Empiricism is the theory that all knowledge comes from sensory experience. According to empiricism, our senses obtain the raw information from the world around us, and our perception of this raw information starts a process whereby we begin to formulate ideas and beliefs. The notion that humans are born with an innate knowledge is rejected, and it is argued that humans only have knowledge that is a posteriori, meaning “based on experience.” Through inductive reasoning of the basic observations provided by the senses, knowledge becomes more complex.

In general, there are three types of empiricism:

Classical Empiricism

This is the form of empiricism associated with John Locke’s tabula rasa theory. The notion of an innate knowledge is completely rejected, and it is assumed that we know nothing at birth. It is only as one begins to experience the world that information is gathered and knowledge is formed.

Radical Empiricism

Radical empiricism was made famous by American philosopher William James. In the most radical forms of empiricism, all of one’s knowledge comes from the senses. One would then be able to conclude from this that the meaning of a statement is connected to experiences that are able to confirm that statement. This is known as the verificationist principle, and it is part of a type of radical empiricism known as logical positivism (which has become an unpopular form of empiricism). Because all knowledge comes from the senses, according to logical positivism, it is not possible to talk about something that has not been experienced. If a statement cannot be linked to experience, that statement is meaningless. For logical positivism to be true, religious and ethical beliefs would have to be abandoned because there are no experiences or observations one could have that would be able to confirm such claims, making them meaningless.

Moderate Empiricism

This form of empiricism, which seems more plausible than radical empiricism, allows for cases where knowledge is not grounded in the senses (though these are still known as exceptions to the rule). For example, in “9 + 4 = 13” we see a truth that does not require investigation. However, any significant forms of knowledge are still solely gained from experience.

RATIONALISM

Rationalism is the theory that reason, not the senses, is where knowledge originates. Rationalists claim that without having principles and categories already in place, humans would not be able to organize or interpret the information provided by the senses. Therefore, according to rationalism, humans must have innate concepts and then use deductive reasoning.

Rationalists believe in at least one of the following:

The Intuition/Deduction Thesis

This thesis states that there are some propositions that are known as a result of intuition alone, while other propositions can be known by being deduced from an intuited proposition. According to rationalism, intuition is a type of rational insight. Through deduction, we are able to arrive at conclusions from intuited premises by using valid arguments. In other words, the conclusion has to be true if the premises on which the conclusion is based are true. Once one piece of knowledge is known, one can then deduce others from that original knowledge.

For example, one can intuit that the number 5 is a prime number and less than 6, and then one can deduce that there is a prime number that is less than 6. Any knowledge that is gained from the intuition/deduction thesis is a priori, meaning it has been gained independent of the senses, and rationalists have used it to explain mathematics, ethics, free will, and even metaphysical claims like the existence of God.

The Innate Knowledge Thesis

This thesis states that, as part of our rational nature, we have knowledge of some truths within a particular subject. Like the intuition/deduction thesis, the innate knowledge thesis states that knowledge is acquired a priori. According to this thesis, however, knowledge does not come from intuition or deduction; rather, it is just part of our very nature to have it. The source of the knowledge depends upon the philosopher. While some rationalists believe this knowledge comes from God, for example, others believe it to be the result of natural selection.

The Innate Concept Thesis

This theory states that as part of our nature, humans have concepts that they employ in a specific subject. According to the innate concept thesis, some knowledge is not the result of experience; however, sensory experience can trigger the process that brings this knowledge to our consciousness. While experience can act as a trigger, it still does not provide concepts or determine what the information is. This concept is different from the innate knowledge thesis because here, knowledge can be deduced from innate concepts. With the innate concept thesis, the more removed a concept is from experience, the more plausible it is to claim it as innate. For example, a concept on geometric shapes would be more innate than a concept on experiencing pain because it is further removed from experience.

While empiricism and rationalism present two different explanations for the same question, the answers are sometimes not as black and white. For example, philosophers Gottfried Wilhelm Leibniz and Baruch Spinoza, considered to be key figures in the rationalism movement, believed that knowledge could be gained through reason in principle. However, besides specific areas like mathematics, they did not think it was possible in practice.