There are two accepted sources of knowledge, reason and experience. This has been accepted as mainstream since these two sources have undergone scrutiny from scholars in the different fields. There is, however, a third source of knowledge called intuition, mainly used by moral philosophers claiming to have discovered the source of knowledge for moral goodness, where they use the faculty of intuition.
The faculty of reason is construed here as an analytic faculty that is able to deter-mine the truth of analytic statements. Therefore, the truth of knowledge claims made in the formal sciences use the faculty of reason following the framework of coherence within the given system. This is different from the transcendental faculty of reason that the rationalist philosophers, like Descartes, was trying to describe. They conceived of the transcendental faculty of reason as a mind or a faculty that could exist independently of the body. Descartes’ notion of the transcendental faculty of reason stretches this faculty beyond the physical realm which transcends the body and the physical world. Suffice it to say that the analytic faculty of reason as a legitimate source is confined to the ability of a human being to perform his rational functions including the act of thinking and analysis. There is no assumption about the existence of a transcendental mind or substance in this regard. Thus, when one analyzes an analytic statement like, ‘A triangle is a closed plane figure bounded by three sides.’ or ‘A spinster (an old maid) has no mother-in-law,’ one would be able to determine whether the statement is true or false, using reason as an analytic faculty, by employing the coherence theory of truth.
The faculty of experience or sense perception, on the other hand, has to do with the use of the five senses, including sensory extending devices for the purpose of verifying our empirical claims and as a result, leading to empirical knowledge. Thus, it uses the correspondence theory of truth in verifying the truth of these empirical statements. The empirical sciences rely on the data from the faculty of experience for establishing scientific knowledge. Because of the recognition of the limits of what can be empirically verified by relying solely on observation using the five senses, scientists have found it a necessary tool in the practice of their science to render what is initially unobservable on the observable plane, thus, contributing to its verification in the empirical world.
Thus, the emergence of these sensory extending devices and other operations as a way of extending what can be known in the empirical world. Once they have been rendered as observable, then they are accepted as part of empirical knowledge. Instruments or sensory extending devices have been invented to extend the realm of what we are capable of knowing and perceiving about the world, thus extending the limits of the physical universe to the smallest fragments of matter or molecules as well the vastness of the outer universe and the beyond. For instance, we have the electron microscope, super computers, artificial intelligence, Atacama radio telescopes known as ALMA in Chile, and others.
This is a way of rendering what is initially unobservable observable, through the use of sensory extending devices. They could also be operations like paper and pencil tests, verbal operations and thought experiments as procedures used, for example, in the field of psychology, in order to observe psychological conditions that may not be easily observable using our five senses without the help of these tests or operations. Some of the relevant examples are the psychological examinations used to check and examine psychological states like anxiety, neurosis, schizophrenia, and others. Even the very familiar Intelligence Quotient (IQ) Test is an example of this paper and pencil operations.
The faculty of intuition, as a third source of knowledge, deals with the immediate or direct recognition of self-evident truths. Others call this tacit knowledge which is unmediated by conceptual process. George Edward Moore, is the proponent of intuitionism in ethics. In his article entitled, Principia Ethica (1903), he appealed to the faculty of intuition for the direct or immediate knowledge of the idea of goodness. Moore assumed that the person should be directly acquainted with his object of knowledge which he likened to one’s knowledge of the color yellow. The idea of the good as the object of knowledge is, according to Moore, like the color yellow where no amount of description of the color yellow to someone who is color blind will suffice for him to have knowledge of yellow. In this particular case, one must be directly acquainted with the color yellow. Thus, unlike the two earlier faculties, reason and experience, which are mediated by concept formation and thought processes for truth discovery, intuition does not have such mediating process between the knower and the known or the object of his/her knowledge. Thus, intuitive knowledge is immediate. Perhaps, the closest philosopher that you are familiar with to describe intuition as a process of taking in knowledge is Plato’s theory of knowledge of the Forms and Ideas. It could be that Plato was actually describing the process of intuition in knowing the idea of the Good in his process of the enlightenment of the soul. Thus, his idea of the Good could be known through the faculty of intuition.
Unfortunately, unlike the faculty of reason and experience, intuition, being tacit, unmediated or direct knowledge, there has been no established method of validating or verifying knowledge claims with intuition as its source. That is, ‘you know when you know,’ and everyone can claim that they have the correct intuition! This is precisely the main reason why intuition, as a source of knowledge, could not be recognized and used as widely as reason and experience by many scientists and philosophers.