As George Lakoff and Mark Johnson note, metaphor is pervasive in everyday life, not just in language but in thought and action. Plato, Bacon, Locke, Leibniz, Kant, Hegel, Neurath, Popper, Kuhn were not mainly trying to produce evocative language, but rather to deepen understanding of the nature of knowledge. Empiricist foundationalists (Locke, Hume) took inspiration from wax tablets and white paper. Other epistemologists and philosophers of science have used instead different metaphors to inspire a non-foundationalist picture of knowledge. Coherentist epistemologists have needed metaphors such as boats, crossword puzzles, and neural networks. In the twentieth century, the most influential coherentist metaphor has been Neurath's ship, which he used in arguing against empiricist foundationalism based on protocol statements concerning sense experience. Analogies in philosophy have contributed to the origin and development of epistemological theories.