 The other main role of the principle is to assist us in forming new concepts (this is Maimon’s attempt to have an ars invendi ). Here again, the principle provides us only with a negative criterion. If we ask ourselves: what are the possible determinations of ‘line’, the principle would not tell us that ‘straight’ is such a determination. Only once we suggest ‘straight’ as such a determination, could the principle evaluate — and in this case, approve — the relation of ‘straight’ to ‘line’.