Thus far, based on Hume‟s notion of empiricism, we have assumed that our senses furnish us with knowledge of the physical world external to us and that the sense data generated by physical objects and which we get impressions from are what guarantee the existence of these objects and through which we have knowledge of them. The conclusion of Hume from this is that “we cannot have any knowledge beyond experience.”15 But before we take this Hume‟s position, hook, line and sinker let us ask ourselves, are what the senses furnish us with absolutely certain that they cannot be doubted, that is, are there no limitations in sense experiences as providing us with knowledge?.
Teleguided by this question, we begin to enquire critically to ascertain the certainty of knowledge that comes through the senses and when through with this critical enquiry, we discover that what we call perception is not only dependent on the sense data or impressions generated by an object, but is at least in part, dependent on the nature of our sensory organs, we therefore become aware that there are limitations to the senses as sources of knowledge and from this, our doubt as regards the certainty of knowledge that comes through the senses starts. Each individual is unique and because of this, has unique senses and therefore perceive uniquely. “If our eyes were different, what we see would be different, if our taste buds were different, so would be the taste we have, what right then have we to assume that
187 we see or taste things the way they really are? In fact, how could we possibly know how things really are? Or what they are really in themselves.”16
As different individuals have different sensory organs, no two individual can therefore perceive one thing exactly the same way and hence this is so, whose perceptions should be accepted as the real one? This implied thus that, “if two persons cannot have the very same experience, and if the world of their language is defined by reference to their experiences, then the suppositions of mutual intelligibility are distinctly shaky.‟‟17 This is because, each individual perception is relative to him and no one can impose his perception on others.
Therefore, “as long as the content of our perception depends so much on the nature of the perceiving organ, and as long as we are unable to shed our perceiving organs as we do spectacle, to try out other ones, how can we be so sure that we are perceiving things as they are … indeed, do we have any right to say what the physical world is really like at all.”18 Besides differences in perceptions in different individuals, there are still cases of wrong perceptions when it is only one individual involved. On this note, let us consider illusion or optical illumination, in which case, one does not perceive things as they are. What we are then referring here include situations such as a stick, half immersed in water, looking bent though in reality it is straight, the trees on the distant mountain side looking grayish blue, though they are dark green, what of electricity cable on poles that look as if they meet each other in the distance whereas in reality, they do not meet because they run parallel to each other? In these situations, if we should rely on what the senses give us, we will be misled; it thus becomes clear that in sense perceptions, we are sometimes misled. Therefore, “it is a common place that I cannot have everything that I hear or that I read … none even what I apparently see, most of what I see or hear in this way are hallucinations.”19
188 In some cases also, our senses furnish us with appearance not reality, in this case, we perceive things that are not there. When one presses his eyeballs, he sees things double when they are of course one, a person can equally see a pool of water in the distant side of the road and yet when he gets to that point, he finds out there is no such thing in reality. These are hallucinations, the things we perceive in this case, do not exist, yet we perceive them. It is our senses that furnish us with such non-existences, which are very misleading. Therefore,
In daily life, we assume as certain many things which, on a closer scrutiny, are found to be so full of apparent contradictions that only a great amount of thought enables us to know what it is that we really may believe. In the search of certainty, it is natural to begin without present experience, and in some sense, no doubt knowledge is to be derived from them. But any statement as to what it is that our immediate experience, made us know is very likely to be wrong.20
Thus, we are now aware that our senses mislead us sometimes and having known this, one begins to wonder whether the whole physical world is not as Descartes suspected “one gigantic hallucination” in which case, we are constantly being deceived that it is there. All these errors in perception must have promoted Descartes doubts which led him to the suspicion that there may be an evil demon at work who arranges things in a way to deceive us into thinking that their physical things exist when they are not. Descartes therefore, argued that, “knowledge may be illusory because, it comes from a demon that is able to deceive men by making them think they are experiencing the real world when they are not.”21
Based on these limitations that have been pointed out, one discovers that the senses cannot be completely relied upon as furnishing us with reality. Yet in spite of all these limitations, David Hume held sacrosanct to the senses as the only means of knowing reality because, they are the only organs through which we perceive the impressions generated by external
189 objects. His argument seemed to have run thus; those objects that generate impressions are the only things that are real and since it is through the senses that we perceive these impressions, it is therefore through the senses that we can only acquire knowledge of reality.
But based on the limitations we have pointed out, we have discovered that much as we can rely on the senses for the acquisition of knowledge, this reliance must not be in the extreme as David Hume claimed, because most times, the senses furnish us with appearance that are not reality.
We should also note that Hume‟s belief of existence of his own impressions and ideas is emphatically a skeptical system. Hume‟s belief of the existence of impressions and ideas is little supported by any reason of critical mind. Hume‟s phenomanalistic epistemology is a traditional empiricism with a radical content.
Alluding to Hume‟s conceptions of impressions and ideas is dangerous. A thorough and consistent skeptic will never therefore yield to this Humean tradition of empiricism. We are sometimes misled into sensory error. Hume‟s treatment of impression and idea could so far be seen as problematic.
Hume had earlier distinguished impressions from ideas on the basis of their force and vivacity and had used the word violence in doing so. The Humean assumption of traditional empiricism of impressions, beliefs, passions, ideas, emotions constitute psychological generalizations.
Sensism generally cannot explain all knowledge; sense knowledge itself must have a deeper foundation than the human person himself as the substance who senses. When he rejected causality, he made no provision for certitude for any knowledge including the empirical. He based all human inquiry on the shaky foundations of brute sensibility, ephemeral empiricism
190 and shifting associationism when he argued only for habitual association of ideas for all beings, knowledge and relationships.