The powerful image conjured up by Neurath, in his Anti-Spengler (1921), whereby the body of knowledge is compared to a boat that must be repaired at sea: ‘we are like sailors who on the open sea must reconstruct their ship but are never able to start afresh from the bottom…’. Any part can be replaced, provided there is enough of the rest on which to stand. The image opposes that according to which knowledge must rest upon foundations, thought of as themselves immune from criticism, and transmitting their immunity to other propositions by a kind of laying-on of hands. See also foundationalism, method of doubt.