 While the analytic/synthetic distinction appears to be justifiable in modeling important properties of languages, the observational/theoretical distinction does not fare equally well. Within logical positivism, observation language was assumed to consist of names and predicates whose applicability or not can be ascertained, under suitable conditions, by means of direct observation (such as using names and predicates for colors, shapes, sounds) or relatively simple measurement (names and predicates for heights, weights, and sizes, for example). This was an epistemic position, of course, since it was sorting them out based upon their accessibility by means of experience. Both theoretical and dispositional predicates, which refer to non-observables, posed serious problems for the positivist position, since the verifiability criterion implies they must be reducible to observables or are empirically meaningless. Karl Popper (1965, 1968), however, would carry the argument in a different direction by looking at the ontic nature of properties.