… Between the deliberate falsehood and the disinterested inaccuracy it is very hard to distinguish sometimes… To deceive deliberately – that is one thing. But to be so sure of your facts, of your ideas and their essential truth that the details do not matter – that, my friend is a special characteristic of particularly honest persons… She looks down and sees Jane Wilkinson in the hall. No doubt enters her head that it is Jane Wilkinson. She knows it is. She says she saw her face distinctly because – being so sure of her facts – exact details do not matter! It is pointed out to her that she could not have seen her face. Is that so? Well, what does it matter if she saw her face or not – it was Jane Wilkinson… She knows. And so she answers questions in the light of her knowledge, not by reason of remembered facts. The positive witness should always be treated with suspicion, my friend. The uncertain witness who doesn’t remember, isn’t sure, will think a minute – ah! yes, that’s how it was – is infinitely more to be depended upon!
Hercule Poirot in Lord Edgware Dies by Agatha Christie, 1933.
The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.
Werner Heisenberg, Uncertainty Paper, 1927.
In 1933, Hercule Poirot demonstrates the futility of “positive knowledge”, how it goads its (supposed) possessor into ignoring the details, and since facts not yet framed in a semantic context always assume the character of details, into ignoring the facts, hence bending, distorting, recreating and misrepresenting them in order to conform to a pre-existing, a priori “knowledge”. Werner Heisenberg, however, precisely six years before Poirot, demonstrates the impossibility of such knowledge, basing his argument not on the undesirable consequences of presumed positive knowledge, but rather on its premises: “But what is wrong in the sharp formulation of the law of causality, “When we know the present precisely, we can predict the future,” is not the conclusion but the assumption. Even in principle we cannot know the present in all detail.” What Heisenberg suggests actually coincides with Poirot’s argument: The more we go into further detail in our investigation of physical phenomena, the less precise we get. The problem arises when we do not acknowledge this fact and believe our knowledge (of larger, more general physical phenomena) to be absolute, applicable to everything in existence, from the movement of galaxies to the movement of photons and electrons. Therefore, the more we believe our presumed knowledge to be certain, the more likely we are to ignore the minute details (the momentum and/or the position of an electron, for instance) which do not conform to this knowledge. To be sure, the 1926 discussion between Heisenberg and Einstein makes a specification as to the nature of this “knowledge”: While Heisenberg tries to specify observable/knowable phenomena with regard to measurability, Einstein challenges him to suggest that observability is directly connected with conformity to a certain theory:
Heisenberg: “One cannot observe the electron orbits inside the atom. […]but since it is reasonable to consider only those quantities in a theory that can be measured, it seemed natural to me to introduce them only as entities, as representatives of electron orbits, so to speak.”
Einstein: “But you don’t seriously believe that only observable quantities should be considered in a physical theory?”
“I thought this was the very idea that your Relativity Theory is based on?” Heisenberg asked in surprise.
“Perhaps I used this kind of reasoning,” replied Einstein, “but it is nonsense nevertheless. […] In reality the opposite is true: only the theory decides what can be observed.”
Isn’t this exactly what Poirot was criticizing? To bend observable facts in order for them to conform to a pre-conceived knowledge, of a certainty? It seems to be so, unless we take into account a (seemingly) slight shift in terminology: While Poirot is talking about knowledge (even positive knowledge) Einstein is referring to theory, that is, theoria, that is, a gaze, an outlook, an Anschauung. Theory, in the most basic sense of the term, is the way you look at things, and therefore, it goes without saying that it “decides what can be observed.”
Knowledge, on the other hand, is sophia, something arrived at, and once you arrive there, there is no room for uncertainties: So if details (facts) tend to create unwanted uncertainties, it goes without saying that you should ignore or distort them. Theory is based on uncertainties; the gaze shifts, wanders, wonders, takes in new data, changes, mutates: it represents the uneasy equilibrium of a priori and a posteriori. Positive knowledge, on the other hand, once established, becomes fixed; it doesn’t look anymore, it tells facts what they ought to be: it represents the hegemony of a priori over a posteriori. In short, once the theoretical act coagulates into preconceived knowledge and loses its self-reflexivity, knowledge becomes a risk, rather than an asset, for further knowledge.
In this sense, positive knowledge, that is, knowledge unquestionably certain of itself, has the possibility of becoming the bedrock of what we today call Fundamentalism, once the gaze is fixed. But wait, the uncertain witness will say, isn’t the same thing also the basis of the Enlightenment, what we know today as the diametrical opposite of Fundamentalism? Nonsense, the positive witness will answer, the same thing cannot be the basis of two diametrically opposite entities, can it now? The uncertain witness remains ambiguous and demands (or requests, depending on their predilection) a further examination of the concepts of “Fundamentalism” and “Enlightenment”.
 Werner Heisenberg, “The Uncertainty Paper”, in Quantum Theory and Measurement, eds. John Archibald Wheeler & Wojciech Hubert Zurek; Princeton, NJ: Princeton University Press, 1983.
 Werner Heisenberg, Der Teil und das Ganze, R. Piper & Co., Munich (1969). Translation by G. Holton.