  Conventionalist deep-level theories of the world are chosen from among alternative ways of observing phenomena. Although theories revealing the world structure are not directly provable or disprovable by means of observation or experiment, conventionalists might maintain their chosen theory even in the face of counter-evidence. They therefore avoid changes of theory. Any move to a new theory is not taken on the basis of new evidence, but because a new theory seems to be simpler, more applicable or more beautiful. Laws of nature are generally understood as being unrevisable (O'Hear 1995, 165).  The famous debate, sparked by Thomas Kuhn, on paradigmatic and non-paradigmatic science and theory is relevant here. Bacon's position—open to scientific progress—is nearer to Kuhn than to Duhem or Poincaré. For Bacon, “anticipation of nature” (as a mode of “conventionalism”) produces obstacles to the progress of knowledge. Traditional methods shun speculation concerning things which are not immediately visible; Bacon's speculation, however, is an element of “interpretation of nature”. He presupposes hypothetical theories, but these do not go beyond the collected data. His acceptance of hypotheses is connected with his rejection of “anticipation of nature”. Thus, hypotheses are related to the axioms of “interpretation of nature”, which go beyond the original data. The amount of established facts is not identical with that of possible data (Gillies 1998, 307). Anticipation is rejected, only if it “flies from the senses and particulars to the most general axioms” (OFB XI, xxv).  Because of the dangers of premature generalization, Bacon is careful about speculations and rigorously rejects any dogmatic defense of them and the tendency to declare them infallible.