In Philosophy during the 20th century a lot of progress was made in the Continental branch, which is just the continuation of Western philosophy in Europe, as distinguished from the Analytically Philosophy branch which in the eyes of some was a regression in which philosophy just became an anti-philosophical handmaiden of Science.This came from a real need on the part of academics due to McCarthyism to distance themselves from Hegel because of the misuse of Hegel by Marx. From the Analytical point of view Western Philosophy stopped at Kant and then went to Frege and then to Early Wittgenstein and then on from there to Quine, Putnam, Moore etc. until you get to Kripke, Lewis, and Branden.
On the other hand, Continental Philosophy, which is really European Philosophy continuing unperturbed based on Husserl’s Phenomenology, Heidegger’s Nazi Philosophy (He spent the war trying to show his philosophy was a better basis for Nazism than Nietzsche’s philosophy) taken up by communist (resistance) intellectuals in after the war. These communist intellectuals were the only ones in Europe not hogtied by Soviet domination. This meeting of radical opposites, Nazism and Communism in the intellectual sphere produced a renaissance in Philosophy in France, the advances of which we are still reeling from. So deep are the ideas, more or less commensurate with String theory in Physics, that our cultural tradition has not even started absorbing it more generally yet. I studied it in the Seventies when the translations first started appearing. I soon realized that it was pertinent to my study of Philosophy of Science which focused on the facticity of emergent events within our tradition. I came to understand that the various kinds of Being proposed by the Continental Philosophers is best understood by Russell’s Higher Logical Type Theory something also abandoned by Analytical Philosophy.
Heidegger in Beng and Time based on the Later Husserl distinguishes between two equiprimordial modes of being-in-the-world (Dasein) which are present-at-hand (Pure Being) and ready-to-hand (Process Being). Thinking that these are essentially the difference between Theoretical and Practical reason. But this opened Pandora’s box and Heidegger himself got worried when he discovered the third kind of Being, which he called -B-e-i-n-g- crossed out. Derrida took this up and called it Differance (Differing and Deferring). Then Merleau-Ponty also discovered it independently and called it the Hyper Dialectic between Being (Heidegger’s second kind of Being, i.e. Process Being, and Nothingness of Sartre. Merleau-Ponty contrasted the expansion of being-in-the-world of Hyper Being with the contraction of being-in-the-world modality of Wild Being. And eventually we come to realize that there is a final kind of Being called Ultra Being after much resistance to this idea, that there is a singularity of Being at the fifth meta-level in existence. Plato had identified the first two kinds of Being in the Pre-socratic philosophies of Parmenides and Heraclitus. But in the Timaeus he also identifies a third kind of Being, and thus makes clear that he knew about the third meta-level of Being.However this knowledge was lost in our tradition until it was rediscovered by Heidegger and popularized by Derrida. Other philosophers like Deleuze went on to try to build philosophies at the fourth meta-level of Being. This whole development has gone full circle with Badiou claiming that Being is the same as Set Theory which like almost all math is purely present-at-hand.
In my first dissertation I used the kinds of Being to attempt to understand emergent events within our tradition at any level of scope, such as facticity, theories, paradigms, epistemes, ontoi, existences, and absolutes. But I was knocked out when I eventually discovered that it was the kinds of Being that distinguished the gods in the Indo-European tradition as defined by Dumazile. This meant that this structure was extremely persistent despite the fact that the tradition is wracked by Emergent Events. This rediscovery of a deeper understanding of our own tradition, that was lost in oblivion until Continental came along, is a major change which has not made its effects felt at yet but I predict that it will transform our worldview in this century.
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http://www.quora.com/The-Big-Philosophical-Questions/What-were-the-greatest-intellectual-achievements-of-the-20th-century-in-science-and-mathematics