Sensory perception is the reception and interpretation of knowledge through sight, hearing, touch, smell and taste. These five senses provide us with information as to what there is in the world and allow us to be aware of certain qualities of these things. It is exclusively through sensory perception that humans acquire knowledge of the external world, as all other ways of knowing are direct results of it. Emotion is chemical releases or nervous reactions in the body, both of which must be perceived, caused by the perception of an external event.
Language is an external transmission of knowledge and therefore must be perceived to be utilized. Reason is the deduction or induction of knowledge and therefore must be based on an observation, which must also be perceived. Can this way of knowing be trusted? To determine the extent to which they can, I will examine the imperfections of the senses, and how reason and emotions may affect perception. Avicenna defined truth as, “what corresponds in the mind to what is outside it”. Therefore, if the mind knows exactly what a table consists of at the most basic level, then one knows the truth of the table lying in front of them.
This leads to the problem of the imperfection of our senses. The sensation of sight tells us that a leaf from a plant is a relatively smooth, flat, whole object and appears to be composed of two consistent materials, the veins and the epidermis. This is a leaf in the mind of an onlooker without any previous knowledge on the subject or any special observational equipment. However, a biologist who has studied the leaf knows that it is much more complicated than this. He knows that there are five ‘layers’ throughout a leaf.
He knows that the most external layer is the cuticle, followed by the epidermis, palisade mesophyll, the spongy mesophyll and finally the lower epidermis. Another biologist who has studied each of these layers through a microscope knows that each layer consists of groups of cells, all individual beings which interact to form what appears to be a single organism, and that the surface of the leaf is far from smooth. A chemist knows that each part of each cell, and thus the entire leaf, is in fact a mesh of molecules, atoms and sub-atomic particles, rather than a whole material.
In this case, our senses tell us that the leaf is one thing, when in fact it is another, what is in the mind does not correspond to what is outside it. Without any tools to enhance our senses, what we perceive is only a very small part of the truth, a simplified version. This idea is summarized by Alfred Whitehead who claims that “there are no whole truths; all truths are half-truths. ” Despite not being able to acquire the whole truth through our senses, we can always rely on them to accomplish their role. Sight is the recognition of different wavelengths of light, not a manner of acquiring knowledge of the true composition of an object.