This is Part 10 of my series on science. Here are the other parts: Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8, Part 9, Part 10, and Bibliography.

Unbelievers take many things for granted. They think that, from a number of glances, they can understand reality. This assumption on the unbeliever’s part has been growing in popularity within Christian and Non-Christian debates. The main contention is to ask whether that is truly the case. Do we from mere observations acquire a comprehensive picture of reality?
Let us look at a brown table. We notice that it has the properties of a table. You can describe its size, color, shape, width, etc. Can you doubt that you are seeing the table for what it is? Are you misidentifying these qualities? Could it be a mirage? Or maybe it is a hallucination? It may be that our mind distorts the sense-datum that comes through our senses. How do you know how to distinguish between appearances and reality? How do we know the “things in themselves” over against how they appear? You may find these questions silly and not worth your consideration. That puts you at odds with many philosophers that have considered these questions since the ancient Greeks. Here is one such Philosopher:

To make our difficulties plain, let us concentrate attention on the table. To the eye it is oblong, brown, and shiny, to the touch it is smooth and cool and hard; when I tap it, it gives out a wooden sound. Anyone else who sees and feels and hears the table will agree with this description, so that it might seem as if no difficulty would arise; but as soon as we try to be more precise our troubles begin. Although I believe that the table is ‘really’ of the same colour all over, the parts that reflect the light look much brighter than the other parts, and some parts look white because of reflected light. I know that, if I move, the parts that reflect the light will be different, so that the apparent distribution of colours on the table will change. It follows that if several people are looking at the table at the same moment, no two of them will see exactly the same distribution of colours, because no two can see it from exactly the same point of view, and any change in the point of view makes some change in the way the light is reflected. For most practical purposes these differences are unimportant, but to the painter they are all-important: the painter has to unlearn the habit of thinking that things seem to have the colour which common sense says they ‘really’ have, and to learn the habit of seeing things as they appear. Here we have already the beginning of one of the distinctions that cause most trouble in philosophy—the distinction between ‘appearance’ and ‘reality’, between what things seem to be and what they are. The painter wants to know what things seem to be, the practical man and the philosopher want to know what they are; but the philosopher’s wish to know this is stronger than the practical man’s, and is more troubled by knowledge as to the difficulties of answering the question.
To return to the table. It is evident from what we have found, that there is no colour which pre-eminently appears to be the colour of the table, or even of any one particular part of the table—it appears to be of different colours from different points of view, and there is no reason for regarding some of these as more really its colour than others. And we know that even from a given point of view the colour will seem different by artificial light, or to a colour-blind man, or to a man wearing blue spectacles, while in the dark there will be no colour at all, though to touch and hearing the table will be unchanged. This colour is not something which is inherent in the table, but something depending upon the table and the spectator and the way the light falls on the table. When, in ordinary life, we speak of the colour of the table, we only mean the sort of colour which it will seem to have to a normal spectator from an ordinary point of view under usual conditions of light. But the other colours which appear under other conditions have just as good a right to be considered real; and therefore, to avoid favouritism, we are compelled to deny that, in itself, the table has any one particular colour.
The same thing applies to the texture. With the naked eye one can see the grain, but otherwise the table looks smooth and even. If we looked at it through a microscope, we should see roughnesses and hills and valleys, and all sorts of differences that are imperceptible to the naked eye. Which of these is the ‘real’ table? We are naturally tempted to say that what we see through the microscope is more real, but that in turn would be changed by a still more powerful microscope. If, then, we cannot trust what we see with the naked eye, why should we trust what we see through a microscope? Thus, again, the confidence in our senses with which we began deserts us. The shape of the table is no better. We are all in the habit of judging as to the ‘real’ shapes of things, and we do this so unreflectingly that we come to think we actually see the real shapes. But, in fact, as we all have to learn if we try to draw, a given thing looks different in shape from every different point of view. If our table is ‘really’ rectangular, it will look, from almost all points of view, as if it had two acute angles and two obtuse angles. If opposite sides are parallel, they will look as if they converged to a point away from the spectator; if they are of equal length, they will look as if the nearer side were longer. All these things are not commonly noticed in looking at a table, because experience has taught us to construct the ‘real’ shape from the apparent shape, and the ‘real’ shape is what interests us as practical men. But the ‘real’ shape is not what we see; it is something inferred from what we see. And what we see is constantly changing in shape as we move about the room; so that here again the senses seem not to give us the truth about the table itself, but only about the appearance of the table.
Similar difficulties arise when we consider the sense of touch. It is true that the table always gives us a sensation of hardness, and we feel that it resists pressure. But the sensation we obtain depends upon how hard we press the table and also upon what part of the body we press with; thus the various sensations due to various pressures or various parts of the body cannot be supposed to reveal directly any definite property of the table, but at most to be signs of some property which perhaps causes all the sensations, but is not actually apparent in any of them. And the same applies still more obviously to the sounds which can be elicited by rapping the table. Thus it becomes evident that the real table, if there is one, is not the same as what we immediately experience by sight or touch or hearing. The real table, if there is one, is not immediately known to us at all, but must be an inference from what is immediately known. Hence, two very difficult questions at once arise; namely, (1) Is there a real table at all? (2) If so, what sort of object can it be?
Bertrand Russell. The Problems of Philosophy (Kindle Locations 260-302). Oxford University Press. Kindle Edition.

Commonsensical response:
The first two responses are to start discussing a person’s different theories of sense perception. The first such theory is Naive Realism, which maintains that we simply look and see the field. That is how we know it is there. The second theory being the Causal Commonsensical view. You may suppose that we receive sense-data only if we have received a causal connection from something exterior to ourselves to cause such sensations to occur. That we see a square field if light bounces off it and connects with our retina. It maintains that our perceptions are causal relations. This implies that we hear things if someone plays music in a proximity to us.
i) The issue is these are only views that tell us how sense perception works and not why it is reliable. It may be true and still be unreliable. How do we know the causal chain is reliably giving us datum?
ii) The other problem is that of optical illusions and hallucinations.

One natural thing to say about what it is for us to see the green field is appealingly brief. We simply see it, in an ordinary way: it is near and squarely before us; we need no light to penetrate a haze or a telescope to magnify our view. We simply see the field, and it may normally be taken to be pretty much as it appears. This sort of view, called naive realism, has been thought to represent common sense: it says roughly that perception is simply a matter of the senses telling us about real things.
The view is naive because it ignores problems of a kind to be described in a moment; it is a form of realism because it takes the objects of perception to be real things external to the perceiver, the sorts of things that are “out there” to be seen whether anyone sees them or not. A more thoughtful commonsense view retains the realism without the naivety. It is quite commonsensical, for instance, to say that I see the field because it is before my open eyes and stimulates my vision, thereby appearing to me as a green, rectangular shape. Stimulating my vision is a causal relation. For instance, the field, by reflecting light, causes me to have the visual experience that is part of my seeing that very field. Moreover, the field apparently must cause my visual experience if I am to see it. As the more thoughtful commonsense view specifies that the object of perception must be a real external thing, we might call it a perceptual realism. Most—but not all—theories of perception incorporate perceptual realism. …
We can make progress by pursuing the question of why naive realism is naive. Suppose there is a gray haze that makes the green field look gray. Or suppose the mouth of the cup I am holding appears, from a certain angle, as if it were an ellipse rather than a circle, or feels warm only because my hand is cold. These are perceptual illusions, roughly perceptual experiences that (in the way illustrated) misrepresent the object of perception. They illustrate that things are not always as they seem. The cup is round and at room temperature. Now imagine that the field burns up. I sorely miss its rich green and the spruce and maple, and on waking from a slumber in my chair I have a hallucination, roughly a sense experience qualitatively like a perceptual one but not of an external object. In this case, my (hallucinatory) visual experience is just as it would be if I were seeing the field. Here the grass I seem to see is not there at all. The point is not that something I see is not as it seems (as in the case of illusion) but that there seems to be something where there is nothing. With illusion, as illustrated by a partly submerged stick’s looking bent, what is there is perceived distortedly; with hallucination, it appears that something is perceived when nothing is. Illusions and hallucinations are possible for the other senses too. When they occur, we do not just see (or hear, taste, smell, or touch) the object. Either we do not see it as it is or (perhaps) we do not see anything at all. Not everything we perceive is as it appears to be, and naive realism does not explain why.
One way to deal with illusion and hallucination is to stress how they show the need to distinguish appearance from reality. In a visual illusion, one sees something, but it does not appear as it really is, say circular. In a hallucination, nothing need appear to me at all, and if anything does, it is even less what it appears to be than is the object of an illusion, or is not what it appears to be at all: instead of a blue spruce tree’s appearing blue to me, for instance, it is as if the conical section of space where it stood appears “bespruced.”
(Audi, Robert Epistemology: a contemporary introduction to the theory of knowledge — 3rd ed. Pages 38-40).

Inductive response:
The next position that we will look at is the inductive response to the question of whether Sense perception is reliable. That we check substantial amounts of prior sense datum produced beliefs and compare it to the exterior world and see how many beliefs were reliably produced based on Sense-perception.
The simple objection is that this is circular reasoning. How could you ever establish such an inference apart from sense perception? This is noted by one philosopher:

If we try to assess the reliability of SP in this way, however, we immediately run into a roadblock. How do we determine whether the perceptual beliefs in our sample are true? If we do so by taking another look, listen, or whatever, we would seem to be presupposing the reliability of SP to compile evidence for that reliability and so to fall into circularity. Moreover, more complex ways of determining the truth value of perceptual beliefs will run into the same problem, though less directly. The basic point here is that any way we have of determining perceivable facts in the physical world will depend, sooner or later, on what we learn from sense perception. Even when what we appeal to in showing that X is or is not P (that this wine in this bottle is a Chambolle Musigny) is not itself a perceptual report (that the wine in this bottle came from a cask used to store wine made from grapes grown in the commune of Chambolle Musigny), still, in showing that that is the case, we must at some point rely on perceptual reports. We may be relying on various records that detail the historical origin of the wine in this bottle. Not only must we use our eyes to read the reports, but the reports themselves, if valid, were based on observations of the grapes and the wine at various stages of their history.
The Reliability of Sense Perception, Cornell University Press (William P. Alston) pg. 13

Pragmatic response:
This response maintains that the validation of SP is that it allows us to predict and manipulate our circumstances in such a way to control the course of events. We can gather the data from this to create a framework of lawlike generalizations that we can use for prediction and control.
This in no way answers the problem. The issue is that a pragmatic response ignores the fact that it is an epistemic challenge. The fact it works doesn’t entail that it is providing true sense datum. For example, say every time we saw a lion in the distance that instead of a lion an attack helicopter appeared to us. We naturally and pragmatically would survive but based on fraudulent information. The second problem is how do we know that our predictions are successful? You may say from previous occasions we have this inductive inference. The issue with that response is how do we know we are successful in particular cases?
If we can’t distinguish between appearances and reality, then how do we know there is such a thing as an exterior world?
I do not believe that there exist any ultimately satisfying philosophical arguments that answer these questions in totality. There exist more complicated attempts to answer these questions, but nothing that would ultimately satisfy. However, I do believe that there exist theological answers to these questions that would more than satisfy these demands. If God has created Mankind and blessed us with reliable sense perception capabilities and the environments to correspond with such faculties, then we can trust that our sense is generally reliable. We are designed like radio waves from a radio broadcast to a receiver. God is the radio broadcaster and we are the receivers to receive his revelation. This is another philosophical battle that belongs to the Lord.