Karl Popper rethought the idea of foundationalism being a concrete set of assumptions or beliefs upon which knowledge is built. He related his view metaphorically to a swamp in which pillars or structures are sunk to create foundations. THe swamp implies that the empirical foundation of objective science is nothing absolute. Science and its structure and network of theories are a towering edifice that rises out of a swamp of uncertainty and possibility. The foundations are piers going down into the swamp from above. They do not reach a natural base, rather, they stretch down to the necessary degree to support the edifice of theory above.
Notes from Karl Popper: The Formative Years 1902 – 1945