The major aim of the study reported here was to discover a way of measuring the productivity of derivative patterns or processes, a task which appears never to have been accomplished for any language before. As specific material for the study, two contrasting deadjectival verbal derivative patterns were chosen: the 'inchoative' -eti and the 'factitive' -iti, as occurring in, e.g., rjav 'brown', rjaveti 'to become brown', rjaviti 'to make (someone or something) brown.' The method involved psycholinguistic tests, administered in Ljubljana in 1993—94. The subjects for the tests in 1993 were 186 secondary and 180 post-secondary students. For the 1994 follow-up study the tests were limited to three groups of university respondents, totalling 116 in all. Cues comprised four questions: (1) Ali se po vašem beseda nahaja v knjižni slovenščini? (2) Ali vi to besedo kdaj uporabljate? (3) Ali je ta beseda po vašem možna in razumljiva? (4) Kako pogosto sami uporabljate to besedo? Subjects selected responses on five-point Likert scales; the data were analyzed statistically. As far as productivity is concerned, there are three conclusions. First, it is clear that, at least for these derivative patterns, productivity is a "cline,'' but in two quite distinct meanings of the term. First and most obviously, one process may be synchronically more productive than another. Second, what may be called the productive strength of any one process also varies. To take just two examples from the mean responses to question (3), we see that the cue godneti was assessed, on average, as extremely "possible and understandable," while at the other end of the scale the cue plašeti was assessed, on average, as well nigh impossible and incomprehensible; the remaining cues are strung out along the cline in between the two.