Advocates of Gordon Clark's epistemological position rightly point out that it is impossible for sensation to produce knowledge. It is therefore the case that it is impossible for any investigation which relies upon sensation to produce knowledge. Here are a list of some of the ways in which sensation are fallible, as well as some forms of investigation which rely upon sensation by which we cannot produce knowledge:
1) It is possible that our sensations are the result of illusions, hallucinations or misperceptions of some sort. So the now famous, so-called "Gettier problem":
In his short 1963 paper, “Is Justified True Belief Knowledge?”, Edmund Gettier presented two effective counterexamples to the JTB analysis (Gettier 1963). One of these goes as follows. Suppose Smith has good evidence for the false proposition
Jones owns a Ford.
Suppose further Smith infers from (1) the following three disjunctions:
Either Jones owns a Ford or Brown is in Boston.
Either Jones owns a Ford or Brown is in Barcelona.
Either Jones owns a Ford or Brown is in Brest-Litovsk.
Since (1) entails each of the propositions (2) through (4), and since Smith recognizes these entailments, his beliefs in propositions (2)–(4) are justified. Now suppose that, by sheer coincidence, Brown is indeed in Barcelona. Given these assumptions, we may say that Smith, when he believes (3), holds a justified true belief. However, is Smith's belief an instance of knowledge? Intuitively, Smith's belief cannot be knowledge; it is merely lucky that it is true(Ichikawa, 2013).
2) It is possible that our inferences are fallacious due to confounding variables.
3) Inductive reasoning - James N. Anderson tries to argue that Christianity provides the transcendental preconditions for the reliability of induction: "For the Christian, the reliability of induction is grounded in God's covenant faithfulness (Gen. 8:22; Jer. 33:19-26). Allah has no comparable attribute. Indeed, it would be beneath Allah to bind himself to men with a covenantal promise!" But these passages have nothing whatsoever to do with induction. It is true that people commonly illustrate the problem of induction with reference to the fact that even something as apparently reliable as the sun rising tomorrow may ultimately prove to not be a universal law; but this is not itself the essence of the problem of induction. These passages he cites have nothing whatsoever to do with the problem of induction. They are references specifically to the continuity of creation provided by God's covenant faithfulness. They have nothing to do with epistemology whatsoever. Indeed, not only do these passages in themselves have nothing to do with induction or even epistemology, but the only reason we know that the sun will rise tomorrow is because the Bible tells us that this is the case. This is thus an infallible inference from an infallible epistemological foundation; namely, the Bible.
The case still remains that no matter how many times we confirm a prediction by induction, we have not proven a universal law, and we therefore have not proven that we can infallibly have confidence that our prediction will always be true.
4) Abductive reasoning - "inference to the "best" explanation." There is no criteria by which we can determine what constitutes the "best" explanation. Conclusions, regardless of the degree of probabalistic warrant which we attribute to them, are at best arbitrary.
5) The socially constituted nature of scientific knowledge - Various philosophers of science and sociologists such as Ludwig Fleck, Thomas Kuhn, Paul Feyerabend, Bruno Latour, W.O. Quine, etc. have pointed out that our scientific beliefs are dependent on historically contingent thought paradigms which are liable to change at any given time. In each generation, beliefs which the previous generation or generations regarded as "common sense" or "universal laws" are liable to be routinely discarded upon new scientific 'discoveries.'
6) The fact that beliefs are constituted in and by a web of mutually supporting beliefs, each of which is ultimately ungrounded and therefore unwarranted - This is not true of knowledge in general for the Christian, but it is true of scientific 'knowledge' and and any belief based upon sensation. Quine and Duhem both famously pointed out that belief (for Duhem, this problem was limited to knowledge of physics) in something depends for its support on other beliefs, which themselves either also depend on other beliefs which are themselves further dependent on other beliefs, or which are themselves are taken for granted without warrant. Either way, all beliefs can be traced back, in their ultimate instance, to unwarranted and taken-for-granted assumptions about the world.
7) The fallibilism of the pragmatists - The American pragmatists John Dewey, William James, C.S. Peirce and Friedrich Schiller, and more recently, Richard Rorty, assume a 'fallibilism' according to which any one of our beliefs might be mistaken. Instead, beliefs are merely 'useful' rather than constituting true knowledge:
Pragmatism was a philosophical tradition that originated in the United States around 1870. The most important of the ‘classical pragmatists’ were Charles Sanders Peirce (1839–1914), William James (1842–1910) and John Dewey (1859–1952). The influence of pragmatism declined during the first two thirds of the twentieth century, but it has undergone a revival since the 1970s with philosophers being increasingly willing to use the writings and ideas of the classical pragmatists, and also a number of thinkers, such as Richard Rorty, Hilary Putnam and Robert Brandom developing philosophical views that represent later stages of the pragmatist tradition. The core of pragmatism was the pragmatist maxim, a rule for clarifying the contents of hypotheses by tracing their ‘practical consequences’. In the work of Peirce and James, the most influential application of the pragmatist maxim was to the concept of truth. But the pragmatists have also tended to share a distinctive epistemological outlook, a fallibilist anti-Cartesian approach to the norms that govern inquiry(Hookway, 2013).
Ichikawa, Jonathan Jenkins and Steup, Matthias, "The Analysis of Knowledge", The Stanford Encyclopedia of Philosophy (Fall 2013 Edition), Edward N. Zalta (ed.), URL = <plato.stanford.edu/archives/fall2013/entries/knowledge-analysis/>.
Hookway, Christopher, "Pragmatism", The Stanford Encyclopedia of Philosophy (Winter 2013 Edition), Edward N. Zalta (ed.), URL = <plato.stanford.edu/archives/win2013/entries/pragmatism/>.