 This problematic was only made more challenging by the presence of Ballung-type terms. The method of testing could not be carried out in a logically precise, determinate and conclusive manner, expecting calculability, determinism, omniscience and certainty, as the prevailing ideal of rationality required (Neurath 1913/1983, Neurath 1934/1983 and Cat 1995). Protocol sentences, by virtue of perception terms, could provide certain stability in the permanence of information necessary for the generation of new expressions. But methodologically they could only bolster or shake our confidence. To acknowledge these limitations is a mark of proper rationality—which he opposed to pseudorationality. A loose coherentist view of justification and unification is the only logical criterion available: ‘a statement is called correct if it can be incorporated in this totality’ of ‘existing statements that have already been harmonized with each other’ (Neurath 1931/1984, 66). Reasons underdetermine our actions and thus pragmatic extra-logical factors are required to make decisions about what hypotheses to accept. Thinking requires provisional rules, or auxiliary motives, that fix a conclusion by decision (Neurath 1913/1983). Scientific rationality is situated, contextually constrained by, practical rationality. The system of knowledge is constrained by historically, methodologically and theoretically accepted terms and beliefs, with limited stability, and cannot be rebuilt on pure, secure, infallible empirical foundations. This is the anti-Cartesian naturalism, non-foundationalism, fallibilism and holism of Neurath’s model. This is also the basis for its corresponding conventionalist, constructivist normativity (Uebel 1996 and 2007 and Cartwright et al. 1996). Without the conventions there is no possibility of rationality or objectivity of knowledge. Neurath captured the main features of his doctrine of scientific knowledge in the image of a boat: