Knowledge and truth were considered absolute and immutable by these two, though for very different reasons, which is the complete antithesis to the empirical theories of Popper, Peirce, Kuhn, and James. The progression of knowledge in the face of such certainty could only result in pure growth from previously established claims, as no truth could ever be said to exist that was not thoroughly and absolutely proved by careful extrapolation from a priori conclusions.
Several interesting anthropological occurrences have convinced me that the empirical method, with its possibility for the adjustment of truth based on the framework or paradigm from which the determination of truth is made, is a much better way of understanding truth and the concept of "absolute certainty." Cultures exist that have no concept of, or words for, time. "Yesterday" and "today" are meaningless concepts that do not exist. The extreme difficulty of communication that this presented suggests that immutable and universal truth is a false concept, even when it comes to basic worldview.
Foucault, Pinter, and Truth Differentiated
The four empiricist philosophers discussed above are by no means the only philosophers of the past century to have tackled the notion of truth. They all approached the matter from basically scientific perspectives. As they are primarily concerned with the hunt for empirical evidence and facts, it follows quite reasonably that their conceptions of truth would be based on a scientific -- that is, a cautiously and skeptically certain -- worldview. Other conceptions of truth, of course, come from very different perspectives and lead to different conclusions.
Michel Foucault saw truth as primarily, perhaps even solely, a construct and reflection of the various interconnected power structures that exist in a given moment. Though this is somewhat analogous to Kuhn's concept of cultural/scientific paradigms, Foucault's view is far more politically motivated. There is no conscious manipulation of the paradigm in Kuhn's theory, but this is the hallmark of Foucault's. Playwright and Nobel laureate Harold Pinter's views on truth are similar in perspective to Foucault's, though there are significant differences. He, too, sees truth as something that can only be approached but never fully achieved, but makes a careful and impassioned distinction between truth in art and truth in politics.
This distinction was important, though not quite as explicit, for Foucault as well. In his work Truth and Power, Foucault asserts that knowledge and truth are the result of established and sanctioned discourses. The power structures that maintain and perpetuate these discourses, then, are the creators and arbiters of truth. These discourses extend into every aspect of life and even our sense of self, Foucault argues, meaning that not only is there no such thing as absolute objective truth outside the existing power structures -- as these power structures pervade every aspect of reality, perception, and knowledge -- but there is not even a subjective self that can be defined independently from the surrounding power structures. Not just truth, but reality in general, is created by the power structures that both consciously and unconsciously manipulate truth to their own advantage -- i.e. To their own continued power. Though lacking (a little) in the paranoia, Foucault's conception of truth and power is very Orwellian.
Harold Pinter does not seem to feel as constrained by the power structure he perceives as Foucault. Though his comments concerning the differences of truth in art and in politics lead to the same general (and highly oversimplified) conclusion that power networks do attempt to create their own version of truth, he also sees sense and even a duty in asserting a more objective truth to those in power that perpetuate falsehoods. This at first seems contradictory with Pinter's opening comments that "there are no hard distinctions between what is real and what is unreal, nor between what is true and what is false. A thing is not necessarily either true or false; it can be both true and false."
He goes on in his speech makes a deliberate and carefully constructed differentiation between truth in art and in politics, however, drawing a delineation based on the essentiality of the consequences of uncertainty.
Oddly, both Foucault theory of truth has an interesting corollary with certain aspects of Al-Ghazali's. The Islamic mystic claims that all truth comes from Allah; our perception of reality and even our ability to reason derive from the divine will and/or manifestation. In Foucault's view, Allah would be the metapower structure, with the emendation that this metapower would be more fundamental than the smaller power networks Foucault insists are of greater importance. All truth would be derived from the will of this power, and conceiving of knowledge or indeed anything outside the realm of the power structure -- i.e. Allah -- would be simply absurd. Pinter's view is less analogous with the fundamental aspects of Al-Ghazali's worldview, but it does contain the significant similarity that the perceptions and conclusions drawn in this world are not necessarily to be trusted. Though everything in the world exists because of Allah's will, Al-Ghazali made allowances for men to be fooled, and to fool themselves. This is at the very heart of Pinter's drama, and of his complaint with humanity.
There are very few prominent philosophers in the modern world that believe in absolute and certain truths. Oddly, most of the philosophers who propose more transient and subjective understandings of knowledge and truth necessarily make allowances for frameworks of certainty. That is, knowledge and truth could again be defined in terms of absolute certainty, depending on a change in paradigm or discourse. The progression of knowledge, in both science and philosophy, is not nearly as linear as it is often taken to be. The very idea of progress when it comes to knowledge may prove oxymoronic -- at least, for a time.