  The fundamental problem here is that the inductive gap can be closed only if the premises can somehow be made to entail their conclusion, and Ayer denied that this could be done. Naïve realism tried to do it by making the evidence ‘move up’ to the conclusion – by making it the case that in perception our evidence was directly of physical objects, rather than of sense-data from which physical objects were inferred. This could work, if it did, only for perception, and not for other inductive inferences. Reductive attempts to close the gap tried to make the conclusion ‘move down’ to the premises, as in phenomenalism. Ayer by now thought phenomenalism was unsuccessful in this attempt, and again reductionism would not work for the future cases. In his 1956 he thought that the best we could do was to admit the gap and be content to describe the ways in which we actually went about justifying such inferences.