Some people might suppose that our sensory organs are reliable because they have survival value. But this does not follow logically. Chlorophyll has survival value in plants; but this does not imply that chlorophyll reliably informs the plant about the outside world.
I don’t know anyone, naturalist or theist, who supposes that our sensory organs have survival value because they provide us with energy from sunlight- do you?
You seem to have misunderstood. The question is: "How do we know that our senses are basically reliable[?]"
In the hands of Christian apologists, the act of raising doubts about the validity of the senses is an attempt to cut thinkers off from any epistemological methodology of looking outward as their means of acquiring data which can be used to inform one’s knowledge of reality. Essentially, the concern is here is to undermine one’s confidence in sense perception as such, thus compelling a thinker to adopt a mystical approach of looking inward, to consult one’s emotions, imaginations and wishes which apologists seek to manipulate through the use of degrading characterizations of rationality, shame and guilt, and intellectual bewilderment.
Of course, since this question repeatedly pops up in Lisle’s and other apologists’ attempts to stifle non-Christian thinkers, it may be inferred that Christian apologists simply do not know how to answer it themselves and consequently project this inability of theirs onto their critics. The whole upshot of Lisle’s line of inquiry here seems geared ultimately to elicit a desired reaction from the non-Christian, one which essentially takes the form of “Duh, I donno! Must be God did it!” From here the apologist, sensing that his opponent has been defeated, will predictably push his god-belief as the solution to the exposed point of ignorance.
Many secular philosophers throughout the ages have done little or no better than the apologists’ own appeal to ignorance. The history of western philosophy has no shortage of thinkers who have adopted some degree of skepticism about the senses and other aspects of man’s nature and epistemology. Some have come right out and condemned the senses as dysfunctional devices of deception while others have taken a more tentative approach, supposing that the senses are typically reliable but susceptible to error or distortion. Christian apologists have assimilated many of the arguments and strains of skepticism, not because they have anything of value to offer to philosophy, but because they have found that skepticism, given its anti-rational nature, provides expedient application for apologetic ends. Their concern is not to answer skeptics per se, but to utilize their stolen concepts in persuading non-believers to abandon any and all confidence they may have in their minds so that religious “presuppositions” can take its place.
There’s a simple, straightforward answer to Lisle’s question, namely that the validity of sense perception is axiomatic. The fundamental recognition of the reliability of the senses, then, is essentially the application of the axiom of consciousness to perception as such. Rational philosophy observes that there are three distinct levels of consciousness: the sensory level, the perceptual level, and the conceptual level. The axiom of consciousness – i.e., the formal, explicit recognition of the validity of consciousness as such – entails the recognition of the validity of all three levels of consciousness. Thus one does not “prove” that consciousness (including the perceptual level) is valid since proof as such presupposes the validity of the three levels of consciousness. To ask for a proof of anything is to grant the validity of consciousness already. Consequently, to suggest in any way that the senses are invalid, prone to error, deceptive, distortive, etc., is to commit the fallacy of the stolen concept. This is because such suggestions make use of the very faculty it is seeking to disqualify.
Thus if Lisle insists that one cannot know with certainty that his senses are reliable, he is in effect denying the axiom of consciousness while making use of his own consciousness. Thus he should not object to a simple challenge, namely:
When Lisle suggests that the senses may not be entirely reliable, he is making use of his own consciousness; he is performing a variety of conscious actions, such as choosing, thinking, inferring, directing his thoughts, etc. Thus Lisle implicitly assumes the validity or reliability of his own consciousness. But how does he validate his own consciousness without assuming its validity? If he says that his god validates his consciousness, he is making use of his consciousness in making such a claim, thus assuming the validity of what’s in question. If he says that his god's merely existing is a precondition to the senses' reliability, he is assuming the validity of his own consciousness and thereby again begging the question. If he says that one cannot know this, he is still using his consciousness to come to this assessment and is thus, yet again, implicitly assuming the validity of what he is called to validate. So on what basis does he assume the validity of his own consciousness?
Further examination of the nature of the senses as such, in response to Lisle’s line of inquiry, bears this out. To do this, we need to be willing to identify relevant facts which pertain to Lisle’s question about how we know that the senses are reliable. A fundamental fact about sense perception is that it is a biological function. The sense organs are part of the body of the biological organism which possesses them, and their activity is biological in nature. Thus sense perception, as a biological function, is similar to other biological functions in that they are performed by certain organs and organic systems which the organism possesses.
Consider for example digestion. The Wikipedia article on digestion describes the human digestive process as follows (I have removed the many hyperlinks included in the original text):
In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication, a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes.
After some time (typically 1–2 hours in humans, 4–6 hours in dogs, 3–4 hours in house cats), the resulting thick liquid is called chyme. When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated from the rectum during efecation.
How do we know that digestion is reliable?
Moreover, our digestive systems do what they do automatically, given their nature; they act according to what they are. They are not something we have to guide volitionally: once I have swallowed a slice of an apple that I’ve chewed up, the stomach takes over and does the rest on its own; I do not need to manage the process by some act of oversight. Digestion is not a consciously-regulated process, and its purpose – namely to convert an energy source into a form that the organism’s metabolic system can utilize for its own preservation – is not something that has been consciously installed into the organism’s biology.
From this let me propose a broader principle:
We can know that a biological function is reliable when its activity successfully performs the task that we expect it to perform.
How do we know that the senses are reliable?
The task of the senses is to give us awareness of objects – i.e., awareness of the things we perceive when we look outward at the world around us.
For anyone who may be reading this, there’s no mystery here: the answer is a resounding yes: our senses do successfully give us awareness of objects. This would have to be the case for anyone reading this, for what he is reading would be an object and he would not be able to read it if he did not have awareness of it. Thus an attempt to dispute what I have written here would seem only to confirm the truth of what I have written. But more to the point, it should be noted that if a person is perceiving anything, he is perceiving an object, which can only mean that his senses are performing their task successfully. It is also important to note that, like digestion, the activity of the senses is involuntrary. If my neighbor turns his stereo system up to 11 when I’m trying to take a nap, I cannot choose not to hear it; if I stub my toe on bedroom furniture, I cannot choose to feel pleasure instead of pain.
For the purposes of addressing Lisle’s concern, it does not matter what specifically one is perceiving, or what he might identify the objects of his awareness to be. The specific nature of the object one perceives has no relevant bearing on whether or not one’s senses have successfully given him awareness of it; it could be large or small, blue or orange, round or rectangular, furry or stony, wet or dry, wide or narrow, tall or short, etc. Nor does his identification of what he perceives have any bearing on whether or not his senses have successfully given him awareness of an object. Identification of an object one perceives is distinct from merely perceiving it (this distinction is often what is missed by skeptics pressing the kind of challenge Lisle has raises against his non-believing interlocutors). If he sees an object – say a dog – but identifies at something it is not – say he identifies the dog he perceives as a cat – this does not alter the fact that he perceived something, which can only mean that his senses have successfully given him awareness of some object.
So there are two approaches we can take to answer Lisle’s question. The first approach is philosophical in nature, highlighting the axiomatic nature of the concept of consciousness, thus formally acknowledging the validity and reliability of all three levels of consciousness: the sensory, the perceptual, and the conceptual. Denial of this results in the fallacy of the stolen concept.
The second approach is more scientific, examining the nature of the senses given the task which we expect them to perform, namely awareness of objects. Since the senses do in fact successfully give us awareness of objects, they are reliable, just as digesting a meal indicates the reliability of one’s digestive system. Skeptics often ignore these points since they fail to recognize the distinction between perception and identification. Like digestion, perception is not volitional activity. Both are biological functions, and both need to be understood in this context if any conclusions of value are to be drawn about their validity, reliability or functionality.
by Dawson Bethrick