"The gentleman asserted that sensation plays "a role in knowledge acquisition." How can one come to such a conclusion? Clearly by discovering what the role is? Unless one knows what the role is, one cannot know that there is any role at all. For example, in the case of the large debt of the United States government some economists hold that the deficits play no role in producing unemployment, while other economists assert the contrary. To sustain their position, these latter must show what the role is. If they cannot, then neither can they justify their position. When Prime Minister Menachem Begin resigned his position in Israel, some commentators said that a disturbing event on the battlefield caused it. Later it was generally agreed that he resigned solely for reasons of health. Therefore one cannot logically maintain that sensation plays a role in the acquisition of knowledge without showing precisely what that role is"(Clark, p. 22).
Thus, we see Clark's radical skepticism towards the possibility of sensation or perception producing knowledge. While some Clarkians do argue that the senses do play a functional role, perhaps in the acquisition of knowledge, they greatly emphasize the importance, as they do with all things, of defining its role with precision. So Clark might not necessarily be taken here as utterly repudiating the notion that the senses produce knowledge. Perhaps Clark held that in at least some cases, God can use the senses to impart knowledge to the person, but God's impartation is always the final cause of sensation (as it is for all things).
...the empirical apologists have no plausible candidate at all. When I ask them to show how images can be transformed into abstract concepts, not one of them has even tried to explain. They even refuse to define sensation. Likewise perception. They really have no epistemology at all, and their words, to omit an inapplicable part of a popular quotation, are full of found, signifying nothing(Clark, p. 23)
We see Clark's notorious high-access requirements here. If the senses cannot produce knowledge -- or, if we say it in a way perhaps better accommodated by a Clarkian -- if God cannot use the senses instrumentally to produce knowledge (and I'm not saying that Clarkians would necessarily take such a position) -- it is difficult to see how we can obey God in ordinary situations. For example, if it is possible that my senses are deceiving me into believing that a woman is my wife when she is not really, then it is possible I will be committing adultery with someone who is not my wife. Suppose the government has genetically engineered a twin and replaced my wife with her without my knowledge. I suppose it is possible that such a thing could happen. But unless we can be sure beyond a shadow of a doubt that the woman is indeed my wife, I must always be in doubt when engaging in intercourse with her, and whatever is not from faith (which includes knowledge) is sin(Rom. 14:23).
As far as the supposed necessity of defining our terms is concerned -- Clark is obviously to be commended for philosophical rigor in requiring that our terms be adequately defined. But it is hard to escape the suspicion that he is requiring a greater (indeed, impossible) degree of rigor with respect to sensation and perception that he would when it comes to other philosophical issues, in overreaction to his admirable opposition to logical positivism. I would argue that some terms, such as sensation or perception, are merely primitive terms that remain undefined. One can always challenge one's definition of something on the ground that they must explain the terms that constitute them. For example, if knowledge is justified true belief, I may require that the person define all three of these terms, as well as demand that they define all the terms they use in defining these terms, and so on ad infinitum. There is a point at which we must eventually rest content with the primitivity of a term. For example, "Person", "Nature", and so on, are not exhaustively defined in the relevant councils which affirm the Trinity. But is such a thing really necessary? When it comes to sensation, why is it problematic to simply affirm that sensation and perception refer to "the act of God using the eyes, nears, nose, mouth and body to impart knowledge to us"? Is it inadequate to simply affirm that a "Person", with respect to the Trinity, is "whatever it is that God is three of"?
Clark, Gordon. "Lord God of Truth." The Trinity Foundation, 1986. Hobbes, New Mexico.